Revert "Introduce a cmake module to figure out whether we need to link with libatomic."

This reverts commit r260235. It breaks LLVM's bootstrap when building
with a -gcc-toolchain and the system's gcc installation does not provide
the libatomic library and its headers. We should check whether
LIBCXX_GCC_TOOLCHAIN is set and adjust the flags accordingly.

llvm-svn: 260323

Author: Vasileios Kalintiris

libcxx/cmake/Modules/CheckLibcxxAtomic.cmake

@@ -1,6 +1,5 @@
 include(CheckLibraryExists)
 include(CheckCXXCompilerFlag)
-include(CheckLibcxxAtomic)
 
 # Check compiler flags
 
@@ -18,7 +17,3 @@ check_library_exists(c fopen "" LIBCXX_HAS_C_LIB)
 check_library_exists(m ccos "" LIBCXX_HAS_M_LIB)
 check_library_exists(rt clock_gettime "" LIBCXX_HAS_RT_LIB)
 check_library_exists(gcc_s __gcc_personality_v0 "" LIBCXX_HAS_GCC_S_LIB)
-
-if (NOT HAVE_CXX_ATOMICS_WITHOUT_LIB)
-  set(LIBCXX_HAS_ATOMIC_LIB True)
-endif()

libcxx/cmake/config-ix.cmake

@@ -79,7 +79,6 @@ add_library_flags_if(LIBCXX_HAS_C_LIB c)
 add_library_flags_if(LIBCXX_HAS_M_LIB m)
 add_library_flags_if(LIBCXX_HAS_RT_LIB rt)
 add_library_flags_if(LIBCXX_HAS_GCC_S_LIB gcc_s)
-add_library_flags_if(LIBCXX_HAS_ATOMIC_LIB atomic)
 
 # Setup flags.
 add_flags_if_supported(-fPIC)

libcxx/lib/CMakeLists.txt

@@ -15,7 +15,6 @@ pythonize_bool(LIBCXX_ENABLE_SHARED)
 pythonize_bool(LIBCXX_BUILD_32_BITS)
 pythonize_bool(LIBCXX_GENERATE_COVERAGE)
 pythonize_bool(LIBCXXABI_USE_LLVM_UNWINDER)
-pythonize_bool(LIBCXX_HAS_ATOMIC_LIB)
 
 # The tests shouldn't link to any ABI library when it has been linked into
 # libc++ statically or via a linker script.

libcxx/test/CMakeLists.txt

@@ -172,9 +172,6 @@ def add_cxx_link_flags(self, flags):
             flags += ['-lunwind', '-ldl']
         else:
             flags += ['-lgcc_s', '-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

libcxx/test/libcxx/test/target_info.py

@@ -20,7 +20,6 @@ config.generate_coverage        = "@LIBCXX_GENERATE_COVERAGE@"
 config.target_info              = "@LIBCXX_TARGET_INFO@"
 config.executor                 = "@LIBCXX_EXECUTOR@"
 config.llvm_unwinder            = "@LIBCXXABI_USE_LLVM_UNWINDER@"
-config.use_libatomic            = "@LIBCXX_HAS_ATOMIC_LIB@"
 
 # Let the main config do the real work.
 lit_config.load_config(config, "@LIBCXX_SOURCE_DIR@/test/lit.cfg")