Rework libatomic handling in CMake and LIT.

This patch updates the way libc++ handles checking for libatomic, in part
to prepare for https://reviews.llvm.org/D22073.

Changes:
* 'LIBCXX_HAS_ATOMIC_LIB' is now set whenever libatomic is available even libc++
   doesn't need to manually link it.
* 'LIBCXX_HAVE_CXX_ATOMICS_WITH_LIB' is now used to detect when libatomic
   needs to be manually linked.
* 'LIBCXX_HAS_ATOMIC_LIB' now adds 'libatomic' as a available feature in the
   test suite.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@275759 91177308-0d34-0410-b5e6-96231b3b80d8

cmake/Modules/CheckLibcxxAtomic.cmake

@@ -26,9 +26,9 @@ int main() {
 endfunction(check_cxx_atomics)
 
 check_cxx_atomics(LIBCXX_HAVE_CXX_ATOMICS_WITHOUT_LIB)
+check_library_exists(atomic __atomic_fetch_add_8 "" LIBCXX_HAS_ATOMIC_LIB)
 # If not, check if the library exists, and atomics work with it.
 if(NOT LIBCXX_HAVE_CXX_ATOMICS_WITHOUT_LIB)
-  check_library_exists(atomic __atomic_fetch_add_8 "" LIBCXX_HAS_ATOMIC_LIB)
   if(LIBCXX_HAS_ATOMIC_LIB)
     list(APPEND CMAKE_REQUIRED_LIBRARIES "atomic")
     check_cxx_atomics(LIBCXX_HAVE_CXX_ATOMICS_WITH_LIB)

lib/CMakeLists.txt

@@ -79,7 +79,7 @@ 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)
+add_library_flags_if(LIBCXX_HAVE_CXX_ATOMICS_WITH_LIB atomic)
 
 # Setup flags.
 add_flags_if_supported(-fPIC)

test/CMakeLists.txt

@@ -19,6 +19,7 @@ pythonize_bool(LIBCXX_GENERATE_COVERAGE)
 pythonize_bool(LIBCXXABI_ENABLE_SHARED)
 pythonize_bool(LIBCXXABI_USE_LLVM_UNWINDER)
 pythonize_bool(LIBCXX_HAS_ATOMIC_LIB)
+pythonize_bool(LIBCXX_HAVE_CXX_ATOMICS_WITH_LIB)
 
 # The tests shouldn't link to any ABI library when it has been linked into
 # libc++ statically or via a linker script.

test/libcxx/test/config.py

@@ -290,6 +290,9 @@ class Configuration(object):
         if self.cxx.hasCompileFlag('-fsized-deallocation'):
             self.config.available_features.add('fsized-deallocation')
 
+        if self.get_lit_bool('has_libatomic', False):
+            self.config.available_features.add('libatomic')
+
     def configure_compile_flags(self):
         no_default_flags = self.get_lit_bool('no_default_flags', False)
         if not no_default_flags:

test/lit.site.cfg.in

@@ -22,7 +22,9 @@ 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@"
+config.has_libatomic            = "@LIBCXX_HAS_ATOMIC_LIB@"
+config.use_libatomic            = "@LIBCXX_HAVE_CXX_ATOMICS_WITH_LIB@"
+
 config.libcxxabi_shared         = "@LIBCXXABI_ENABLE_SHARED@"
 
 # Let the main config do the real work.