Added GetRunfilesDir() to be able to reliably determine prelude location under various invocation scenarios

[pk19604014]

One of the scenarios used by the fuzzing framework is to place the binary and its runfiles into a folder, resulting in a directory layout like this:

[temp dir]
fuzzer
fuzzer.runfiles/

Tested:

bazel test -c opt executable_semantics/fuzzing:executable_semantics_fuzzer
bazel build -c opt executable_semantics/fuzzing:executable_semantics_fuzzer + run the binary from various locations

[jonmeow]

Now that I've had some time to check this: can you please provide a repro to show what this change is fixing? That should help me review this.

[pk19604014]

Now that I've had some time to check this: can you please provide a repro to show what this change is fixing? That should help me review this.

$ bazel build -c opt executable_semantics/fuzzing:executable_semantics_fuzzer
$ cd bazel-bin/executable_semantics/fuzzing/
$ ./executable_semantics_fuzzer
...
#0 0x55b9116a4c41 in __sanitizer_print_stack_trace /tmp/llvm-20220302-9880-1faggz0/llvm-project-13.0.1.src/compiler-rt/lib/asan/asan_stack.cpp:87:3
#1 0x55b9115ec5b8 in fuzzer::PrintStackTrace() cxa_noexception.cpp
#2 0x55b9115d05f3 in fuzzer::Fuzzer::CrashCallback() cxa_noexception.cpp
#3 0x7f42da5bf1ff (/lib/x86_64-linux-gnu/libpthread.so.0+0x131ff)
#4 0x7f42da2698a0 in __libc_signal_restore_set signal/../sysdeps/unix/sysv/linux/internal-signals.h:105:3
#5 0x7f42da2698a0 in raise signal/../sysdeps/unix/sysv/linux/raise.c:47:3
#6 0x7f42da253545 in abort stdlib/abort.c:79:7
#7 0x55b9116de5b9 in Carbon::Internal::operator|(Carbon::Internal::ExitingStream::Helper, Carbon::Internal::ExitingStream&) /proc/self/cwd/./common/check_internal.h:59:5
#8 0x55b911770500 in Carbon::AddPrelude(std::__1::basic_string_view<char, std::__1::char_traits >, Carbon::Arena*, std::__1::vector<Carbon::Declaration*, std::__1::allocatorCarbon::Declaration* >) (/usr/local/google/home/pkobyakov/.cache/bazel/_bazel_pkobyakov/0c0c6d5ac7dde4460fd40f446af91e37/execroot/carbon/bazel-out/k8-opt/bin/executable_semantics/fuzzing/executable_semantics_fuzzer+0x374500)
#9 0x55b9116d8b90 in Carbon::ParseAndExecute(Carbon::Fuzzing::CompilationUnit const&) /proc/self/cwd/executable_semantics/fuzzing/executable_semantics_fuzzer.cpp:28:3
#10 0x55b9116dadaa in TestOneProtoInput /proc/self/cwd/executable_semantics/fuzzing/executable_semantics_fuzzer.cpp:42:3
#11 0x55b9116dadaa in LLVMFuzzerTestOneInput /proc/self/cwd/executable_semantics/fuzzing/executable_semantics_fuzzer.cpp:41:1
#12 0x55b9115d1e73 in fuzzer::Fuzzer::ExecuteCallback(unsigned char const, unsigned long) cxa_noexception.cpp
#13 0x55b9115d34d4 in fuzzer::Fuzzer::ReadAndExecuteSeedCorpora(std::__Fuzzer::vector<fuzzer::SizedFile, fuzzer::fuzzer_allocatorfuzzer::SizedFile >&) cxa_noexception.cpp
#14 0x55b9115d3969 in fuzzer::Fuzzer::Loop(std::__Fuzzer::vector<fuzzer::SizedFile, fuzzer::fuzzer_allocatorfuzzer::SizedFile >&) cxa_noexception.cpp
#15 0x55b9115c2b7e in fuzzer::FuzzerDriver(int*, char***, int ()(unsigned char const, unsigned long)) cxa_noexception.cpp
#16 0x55b9115ecd72 in main /tmp/llvm-20220302-9880-1faggz0/llvm-project-13.0.1.src/compiler-rt/lib/fuzzer/FuzzerMain.cpp:20:10
#17 0x7f42da2547fc in __libc_start_main csu/../csu/libc-start.c:332:16
#18 0x55b9115999e9 in _start (/usr/local/google/home/pkobyakov/.cache/bazel/_bazel_pkobyakov/0c0c6d5ac7dde4460fd40f446af91e37/execroot/carbon/bazel-out/k8-opt/bin/executable_semantics/fuzzing/executable_semantics_fuzzer+0x19d9e9)

(missing prelude crash)

[jonmeow]

Please make sure to update the PR title/description before committing, as it's no longer GetRunfilesDir.