Adjust msvc_stdlib_force_include.hpp to handle clang++

Summary: This patch adjusts the newly added `msvc_stdlib_force_include.hpp` so that it also works when used with `clang++`.

Reviewers: STL_MSFT

Reviewed By: STL_MSFT

Differential Revision: https://reviews.llvm.org/D28917

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@292539 91177308-0d34-0410-b5e6-96231b3b80d8

include/__config

@@ -189,7 +189,6 @@
 #  define _LIBCPP_LITTLE_ENDIAN 1
 #  define _LIBCPP_BIG_ENDIAN    0
 #  define _LIBCPP_SHORT_WCHAR   1
-
 // If mingw not explicitly detected, assume using MS C runtime only.
 #  ifndef __MINGW32__
 #    define _LIBCPP_MSVCRT // Using Microsoft's C Runtime library
@@ -197,6 +196,9 @@
 #  if (defined(_M_AMD64) || defined(__x86_64__)) || (defined(_M_ARM) || defined(__arm__))
 #    define _LIBCPP_HAS_BITSCAN64
 #  endif
+# if defined(_LIBCPP_MSVCRT)
+#   define _LIBCPP_HAS_QUICK_EXIT
+# endif
 #endif // defined(_WIN32)
 
 #ifdef __sun__