CMake: -Wno-nested-anon-types for Clang.

In LLVM, -pedantic is not set unless LLVM_ENABLE_PEDANTIC is set.
However, Clang's CMakeLists.txt unilaterally adds -pedantic to the run
line, so we need to disable -Wnested-anon-types explicitly.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@176393 91177308-0d34-0410-b5e6-96231b3b80d8

CMakeLists.txt

@@ -138,6 +138,11 @@ configure_file(
 # Add appropriate flags for GCC
 if (LLVM_COMPILER_IS_GCC_COMPATIBLE)
   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fno-common -Woverloaded-virtual -Wcast-qual -fno-strict-aliasing -pedantic -Wno-long-long -Wall -W -Wno-unused-parameter -Wwrite-strings")
+
+  check_cxx_compiler_flag("-Werror -Wnested-anon-types" CXX_SUPPORTS_NO_NESTED_ANON_TYPES_FLAG)
+  if( CXX_SUPPORTS_NO_NESTED_ANON_TYPES_FLAG )
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-nested-anon-types" )
+  endif()
 endif ()
 
 if (APPLE)