Patch by Xing Xue to improve libc++ support for AIX

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@195144 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/__config b/include/__config
index aa8bc44..874bcc1 100644
--- a/include/__config
+++ b/include/__config
@@ -454,7 +454,6 @@
 #define _LIBCPP_HAS_NO_GENERALIZED_INITIALIZERS
 #define _LIBCPP_HAS_NO_NULLPTR
 #define _LIBCPP_HAS_NO_UNICODE_CHARS
-#define _LIBCPP_HAS_NO_STRONG_ENUMS
 #define _LIBCPP_HAS_IS_BASE_OF
 
 #if defined(_AIX)
@@ -514,7 +513,7 @@
 #define __has_feature(__x) 0
 #endif
 
-#if __has_feature(cxx_explicit_conversions)
+#if __has_feature(cxx_explicit_conversions) || defined(__IBMCPP__)
 #   define _LIBCPP_EXPLICIT explicit
 #else
 #   define _LIBCPP_EXPLICIT