Explicitly specify -Wno-error if LIBCXX_ENABLE_WERROR is false.

libcxx doesn't build with -Werror because of #warnings in its source
code. But when libcxx is built as an external LLVM project, it inherits
LLVM build flags, breaking the build if LLVM_ENABLE_WERROR is enabled.


git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@191814 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/CMakeLists.txt b/CMakeLists.txt
index b8f9a03..d5352fa 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -189,6 +189,9 @@
 if (LIBCXX_ENABLE_WERROR)
   append_if(LIBCXX_CXX_WARNING_FLAGS LIBCXX_HAS_WERROR_FLAG -Werror)
   append_if(LIBCXX_CXX_WARNING_FLAGS LIBCXX_HAS_WX_FLAG -WX)
+else()
+  append_if(LIBCXX_CXX_WARNING_FLAGS LIBCXX_HAS_WNO_ERROR_FLAG -Wno-error)
+  append_if(LIBCXX_CXX_WARNING_FLAGS LIBCXX_HAS_NO_WX_FLAG -WX-)
 endif()
 if (LIBCXX_ENABLE_PEDANTIC)
   append_if(LIBCXX_CXX_WARNING_FLAGS LIBCXX_HAS_PEDANTIC_FLAG -pedantic)