[libclc] Restore linking against dynamic libLLVM for out-of-tree builds

This fixes a regression where building against an installation without
the static libraries would fail. This just reinstates the old behaviour
for out-of-tree builds, assuming that in-tree builds (which still aren't
officially supported) will have the static libraries available. We can
refine this as we move towards supporting in-tree builds.

libclc/CMakeLists.txt

@@ -122,7 +122,11 @@ set(LLVM_LINK_COMPONENTS
   IRReader
   Support
 )
-add_llvm_utility( prepare_builtins utils/prepare-builtins.cpp )
+if(CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
+  add_llvm_executable( prepare_builtins utils/prepare-builtins.cpp )
+else()
+  add_llvm_utility( prepare_builtins utils/prepare-builtins.cpp )
+endif()
 target_compile_definitions( prepare_builtins PRIVATE ${LLVM_VERSION_DEFINE} )
 # These were not properly reported in early LLVM and we don't need them
 target_compile_options( prepare_builtins PRIVATE -fno-rtti -fno-exceptions )