Revert "Move the sanitizer build from LLVM 18 to 19"

This reverts commit a67c5e8.

LLVM 19 has use-after-poison errors under ASAN inside of ClangTool:

==95109==ERROR: AddressSanitizer: use-after-poison on address 0x62100000291a at pc 0x00010994cffc bp 0x00016d742690 sp 0x00016d741e40
WRITE of size 13 at 0x62100000291a thread T0
    #0 0x00010994cff8 in memcpy+0x4c0 (libclang_rt.asan_osx_dynamic.dylib:arm64+0x50ff8)
    #1 0x0001050b7f68 in llvm::StringSaver::save(llvm::Twine const&)+0xf4 (subdoc_unittests:arm64+0x1029fff68)
    #2 0x000102ffc1c8 in void llvm::function_ref<void (llvm::Twine const&)>::callback_fn<clang::CompilerInvocationBase::generateCC1CommandLine(llvm::SmallVectorImpl<char const*>&, llvm::function_ref<char const* (llvm::Twine const&)>) const::'lambda'(llvm::Twine const&)>(long, llvm::Twine const&)+0x2c (subdoc_unittests:arm64+0x1009441c8)
    #3 0x000102fba4e4 in clang::CompilerInvocationBase::GenerateDiagnosticArgs(clang::DiagnosticOptions const&, llvm::function_ref<void (llvm::Twine const&)>, bool)+0x9d4 (subdoc_unittests:arm64+0x1009024e4)
    #4 0x000102fe47b0 in clang::CompilerInvocationBase::generateCC1CommandLine(llvm::function_ref<void (llvm::Twine const&)>) const+0xe80 (subdoc_unittests:arm64+0x10092c7b0)
    #5 0x000102ffd914 in void llvm::function_ref<void (clang::CompilerInvocation&, llvm::SmallVectorImpl<char const*>&, llvm::function_ref<char const* (llvm::Twine const&)>)>::callback_fn<clang::CompilerInvocation::CreateFromArgs(clang::CompilerInvocation&, llvm::ArrayRef<char const*>, clang::DiagnosticsEngine&, char const*)::$_1>(long, clang::CompilerInvocation&, llvm::SmallVectorImpl<char const*>&, llvm::function_ref<char const* (llvm::Twine const&)>)+0x64 (subdoc_unittests:arm64+0x100945914)
    #6 0x000102fa0554 in RoundTrip(llvm::function_ref<bool (clang::CompilerInvocation&, llvm::ArrayRef<char const*>, clang::DiagnosticsEngine&, char const*)>, llvm::function_ref<void (clang::CompilerInvocation&, llvm::SmallVectorImpl<char const*>&, llvm::function_ref<char const* (llvm::Twine const&)>)>, clang::CompilerInvocation&, clang::CompilerInvocation&, llvm::ArrayRef<char const*>, clang::DiagnosticsEngine&, char const*, bool, bool)+0x358 (subdoc_unittests:arm64+0x1008e8554)
    #7 0x000102fe07d0 in clang::CompilerInvocation::CreateFromArgs(clang::CompilerInvocation&, llvm::ArrayRef<char const*>, clang::DiagnosticsEngine&, char const*)+0x64 (subdoc_unittests:arm64+0x1009287d0)
    #8 0x000102f5f85c in clang::tooling::ToolInvocation::run()+0x364 (subdoc_unittests:arm64+0x1008a785c)
    #9 0x000102f625f8 in clang::tooling::ClangTool::run(clang::tooling::ToolAction*)+0xd40 (subdoc_unittests:arm64+0x1008aa5f8)
    #10 0x000102d428a8 in subdoc::run_files(clang::tooling::CompilationDatabase const&, sus::collections::Vec<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>>, llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem>, subdoc::RunOptions const&)+0x750 (subdoc_unittests:arm64+0x10068a8a8)
    #11 0x000102d41a84 in subdoc::run_test(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>, sus::collections::Slice<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>>, subdoc::RunOptions const&)+0x6b8 (subdoc_unittests:arm64+0x100689a84)
    #12 0x00010276b63c in SubDocTest::run_code_with_options(subdoc::RunOptions const&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>)+0x2ec (subdoc_unittests:arm64+0x1000b363c)
    #13 0x00010276af98 in SubDocTest::run_code(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>)+0x2b8 (subdoc_unittests:arm64+0x1000b2f98)
    #14 0x0001027f75a0 in SubDocTest_NamespaceNested_Test::TestBody()+0x2b8 (subdoc_unittests:arm64+0x10013f5a0)
    #15 0x0001092a242c in void testing::internal::HandleSehExceptionsInMethodIfSupported<testing::Test, void>(testing::Test*, void (testing::Test::*)(), char const*)+0xc8 (libgtest.1.13.0.dylib:arm64+0x10a42c)
    #16 0x0001091d9234 in void testing::internal::HandleExceptionsInMethodIfSupported<testing::Test, void>(testing::Test*, void (testing::Test::*)(), char const*)+0x1a0 (libgtest.1.13.0.dylib:arm64+0x41234)
    #17 0x0001091d8fe0 in testing::Test::Run()+0x18c (libgtest.1.13.0.dylib:arm64+0x40fe0)
    #18 0x0001091db5a4 in testing::TestInfo::Run()+0x46c (libgtest.1.13.0.dylib:arm64+0x435a4)
    #19 0x0001091ddeb0 in testing::TestSuite::Run()+0x3f8 (libgtest.1.13.0.dylib:arm64+0x45eb0)
    #20 0x0001091ff73c in testing::internal::UnitTestImpl::RunAllTests()+0xa60 (libgtest.1.13.0.dylib:arm64+0x6773c)
    #21 0x0001092a3a2c in bool testing::internal::HandleSehExceptionsInMethodIfSupported<testing::internal::UnitTestImpl, bool>(testing::internal::UnitTestImpl*, bool (testing::internal::UnitTestImpl::*)(), char const*)+0xc8 (libgtest.1.13.0.dylib:arm64+0x10ba2c)
    #22 0x0001091fe85c in bool testing::internal::HandleExceptionsInMethodIfSupported<testing::internal::UnitTestImpl, bool>(testing::internal::UnitTestImpl*, bool (testing::internal::UnitTestImpl::*)(), char const*)+0x1a0 (libgtest.1.13.0.dylib:arm64+0x6685c)
    #23 0x0001091fe47c in testing::UnitTest::Run()+0x244 (libgtest.1.13.0.dylib:arm64+0x6647c)
    #24 0x000102ba685c in RUN_ALL_TESTS()+0xc (subdoc_unittests:arm64+0x1004ee85c)
    #25 0x000102ba5bd4 in main+0x2bc (subdoc_unittests:arm64+0x1004edbd4)
    #26 0x00019643f150  (<unknown module>)
    #27 0xa2187ffffffffffc  (<unknown module>)

0x62100000291a is located 26 bytes inside of 4096-byte region [0x621000002900,0x621000003900)
allocated by thread T0 here:
    #0 0x00010994f944 in __sanitizer_mz_memalign+0x78 (libclang_rt.asan_osx_dynamic.dylib:arm64+0x53944)
    #1 0x0001966041bc in _malloc_zone_memalign+0x138 (libsystem_malloc.dylib:arm64+0x2c1bc)
    #2 0xf071800196782cd4  (<unknown module>)
    #3 0x1510000102a3830c  (<unknown module>)
    #4 0x000102a38714 in llvm::BumpPtrAllocatorImpl<llvm::MallocAllocator, 4096ul, 4096ul, 128ul>::StartNewSlab()+0x4c (subdoc_unittests:arm64+0x100380714)
    #5 0x000102a38070 in llvm::BumpPtrAllocatorImpl<llvm::MallocAllocator, 4096ul, 4096ul, 128ul>::AllocateSlow(unsigned long, unsigned long, llvm::Align)+0x2d0 (subdoc_unittests:arm64+0x100380070)
    #6 0x0001050b7fe8 in llvm::StringSaver::save(llvm::Twine const&)+0x174 (subdoc_unittests:arm64+0x1029fffe8)
    #7 0x000102ffc1c8 in void llvm::function_ref<void (llvm::Twine const&)>::callback_fn<clang::CompilerInvocationBase::generateCC1CommandLine(llvm::SmallVectorImpl<char const*>&, llvm::function_ref<char const* (llvm::Twine const&)>) const::'lambda'(llvm::Twine const&)>(long, llvm::Twine const&)+0x2c (subdoc_unittests:arm64+0x1009441c8)
    #8 0x000102feb5e4 in denormalizeStringImpl(llvm::function_ref<void (llvm::Twine const&)>, llvm::Twine const&, llvm::opt::Option::OptionClass, unsigned int, llvm::Twine const&)+0xb0 (subdoc_unittests:arm64+0x1009335e4)
    #9 0x000102feb884 in denormalizeStringVector(llvm::function_ref<void (llvm::Twine const&)>, llvm::Twine const&, llvm::opt::Option::OptionClass, unsigned int, std::__1::vector<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>, std::__1::allocator<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>>> const&)+0x1b4 (subdoc_unittests:arm64+0x100933884)
    #10 0x000102fb9d74 in clang::CompilerInvocationBase::GenerateDiagnosticArgs(clang::DiagnosticOptions const&, llvm::function_ref<void (llvm::Twine const&)>, bool)+0x264 (subdoc_unittests:arm64+0x100901d74)
    #11 0x000102fe47b0 in clang::CompilerInvocationBase::generateCC1CommandLine(llvm::function_ref<void (llvm::Twine const&)>) const+0xe80 (subdoc_unittests:arm64+0x10092c7b0)
    #12 0x000102ffd914 in void llvm::function_ref<void (clang::CompilerInvocation&, llvm::SmallVectorImpl<char const*>&, llvm::function_ref<char const* (llvm::Twine const&)>)>::callback_fn<clang::CompilerInvocation::CreateFromArgs(clang::CompilerInvocation&, llvm::ArrayRef<char const*>, clang::DiagnosticsEngine&, char const*)::$_1>(long, clang::CompilerInvocation&, llvm::SmallVectorImpl<char const*>&, llvm::function_ref<char const* (llvm::Twine const&)>)+0x64 (subdoc_unittests:arm64+0x100945914)
    #13 0x000102fa0554 in RoundTrip(llvm::function_ref<bool (clang::CompilerInvocation&, llvm::ArrayRef<char const*>, clang::DiagnosticsEngine&, char const*)>, llvm::function_ref<void (clang::CompilerInvocation&, llvm::SmallVectorImpl<char const*>&, llvm::function_ref<char const* (llvm::Twine const&)>)>, clang::CompilerInvocation&, clang::CompilerInvocation&, llvm::ArrayRef<char const*>, clang::DiagnosticsEngine&, char const*, bool, bool)+0x358 (subdoc_unittests:arm64+0x1008e8554)
    #14 0x000102fe07d0 in clang::CompilerInvocation::CreateFromArgs(clang::CompilerInvocation&, llvm::ArrayRef<char const*>, clang::DiagnosticsEngine&, char const*)+0x64 (subdoc_unittests:arm64+0x1009287d0)
    #15 0x000102f5f85c in clang::tooling::ToolInvocation::run()+0x364 (subdoc_unittests:arm64+0x1008a785c)
    #16 0x000102f625f8 in clang::tooling::ClangTool::run(clang::tooling::ToolAction*)+0xd40 (subdoc_unittests:arm64+0x1008aa5f8)
    #17 0x000102d428a8 in subdoc::run_files(clang::tooling::CompilationDatabase const&, sus::collections::Vec<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>>, llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem>, subdoc::RunOptions const&)+0x750 (subdoc_unittests:arm64+0x10068a8a8)
    #18 0x000102d41a84 in subdoc::run_test(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>, sus::collections::Slice<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>>, subdoc::RunOptions const&)+0x6b8 (subdoc_unittests:arm64+0x100689a84)

It's not immediately obvious what is wrong, maybe a bug in StringSaver.
The StringSaver itself should be on the stack still, I think.

.github/workflows/try.yml

@@ -70,20 +70,20 @@ jobs:
             clang_version: 18,
             installed_clang_version: 16
           }
-
         - {
-            name: "Ubuntu Clang-19 Debug",
+            name: "Ubuntu Clang-18 Sanitizer",
             os: ubuntu-latest,
-            build_type: "Debug",
-            cc: "clang-19",
-            cxx: "clang++-19",
-            clang_version: 19,
+            build_type: "Release",
+            cc: "clang-18",
+            cxx: "clang++-18",
+            clang_version: 18,
             installed_clang_version: 16
           }
+
         - {
-            name: "Ubuntu Clang-19 Sanitizer",
+            name: "Ubuntu Clang-19 Debug",
             os: ubuntu-latest,
-            build_type: "Release",
+            build_type: "Debug",
             cc: "clang-19",
             cxx: "clang++-19",
             clang_version: 19,