[libc++] Fix _LIBCPP_EXPORTED_FROM_ABI when visibility annotations are disabled

Fixes a bug where functions would get exported when building with
-fvisibility=hidden and defining _LIBCPP_DISABLE_VISIBILITY_ANNOTATIONS. No
visibility annotations should be added in this case.

The new logic for _LIBCPP_EXPORTED_FROM_ABI matches that of the other visibility
annotations around it.

Differential Revision: https://reviews.llvm.org/D55664



git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@349080 91177308-0d34-0410-b5e6-96231b3b80d8

include/__config

@@ -715,7 +715,11 @@ typedef __char32_t char32_t;
 #endif
 
 #ifndef _LIBCPP_EXPORTED_FROM_ABI
-#  define _LIBCPP_EXPORTED_FROM_ABI __attribute__((__visibility__("default")))
+#  if !defined(_LIBCPP_DISABLE_VISIBILITY_ANNOTATIONS)
+#    define _LIBCPP_EXPORTED_FROM_ABI __attribute__((__visibility__("default")))
+#  else
+#    define _LIBCPP_EXPORTED_FROM_ABI
+#  endif
 #endif
 
 #ifndef _LIBCPP_OVERRIDABLE_FUNC_VIS