[libcxx] Support the use of compiler-rt in lit tests

[phosek]

Summary

Don't link tests against libgcc when compiler-rt is being used.

[phosek]

ping?

[EricWF]

LGTM. Honestly, I'm surprised we don't already have a way to configure like this.

test/CMakeLists.txt

 pythonize_bool(LIBCXX_ENABLE_EXPERIMENTAL_LIBRARY)
 pythonize_bool(LIBCXX_ENABLE_FILESYSTEM)
 pythonize_bool(LIBCXX_ENABLE_RTTI)
 pythonize_bool(LIBCXX_ENABLE_SHARED)
 pythonize_bool(LIBCXX_BUILD_32_BITS)
 pythonize_bool(LIBCXX_GENERATE_COVERAGE)
 pythonize_bool(LIBCXXABI_ENABLE_SHARED)
 pythonize_bool(LIBCXXABI_USE_LLVM_UNWINDER)
+pythonize_bool(LIBCXX_USE_COMPILER_RT)
 pythonize_bool(LIBCXX_HAS_ATOMIC_LIB)
 pythonize_bool(LIBCXX_HAVE_CXX_ATOMICS_WITH_LIB)
 pythonize_bool(LIBCXX_BUILD_EXTERNAL_THREAD_LIBRARY)
 pythonize_bool(LIBCXX_DEBUG_BUILD)
 
 # By default, for non-standalone builds, libcxx and libcxxabi share a library
 # directory.
 if (NOT LIBCXX_CXX_ABI_LIBRARY_PATH)

test/lit.site.cfg.in

 config.target_triple            = "@TARGET_TRIPLE@"
 config.use_target               = len("@LIBCXX_TARGET_TRIPLE@") > 0
 config.sysroot                  = "@LIBCXX_SYSROOT@"
 config.gcc_toolchain            = "@LIBCXX_GCC_TOOLCHAIN@"
 config.generate_coverage        = "@LIBCXX_GENERATE_COVERAGE@"
 config.target_info              = "@LIBCXX_TARGET_INFO@"
 config.executor                 = "@LIBCXX_EXECUTOR@"
 config.llvm_unwinder            = "@LIBCXXABI_USE_LLVM_UNWINDER@"
+config.compiler_rt              = "@LIBCXX_USE_COMPILER_RT@"
 config.has_libatomic            = "@LIBCXX_HAS_ATOMIC_LIB@"
 config.use_libatomic            = "@LIBCXX_HAVE_CXX_ATOMICS_WITH_LIB@"
 config.debug_build              = "@LIBCXX_DEBUG_BUILD@"
 config.libcxxabi_shared         = "@LIBCXXABI_ENABLE_SHARED@"
 config.cxx_ext_threads          = "@LIBCXX_BUILD_EXTERNAL_THREAD_LIBRARY@"
 
 # Let the main config do the real work.
 config.loaded_site_config = True
 lit_config.load_config(config, "@LIBCXX_SOURCE_DIR@/test/lit.cfg")

utils/libcxx/test/target_info.py

def add_cxx_link_flags(self, flags):
             flags += ['-lpthread']
             if not shared_libcxx:
               flags += ['-lrt']
         flags += ['-lc']
         if llvm_unwinder:
             flags += ['-lunwind', '-ldl']
         else:
             flags += ['-lgcc_s']
+        compiler_rt = self.full_config.get_lit_bool('compiler_rt', False)
+        if not compiler_rt:
             flags += ['-lgcc']
         use_libatomic = self.full_config.get_lit_bool('use_libatomic', False)
         if use_libatomic:
             flags += ['-latomic']
         san = self.full_config.get_lit_conf('use_sanitizer', '').strip()
         if san:
             # The libraries and their order are taken from the
             # linkSanitizerRuntimeDeps function in
             # clang/lib/Driver/Tools.cpp