[libc++] Drop support for CRTs older than VS 2015

LLVM dropped support for Visual Studio versions older than 2015 quite
some time ago, so I consider it safe to drop libc++'s support for older
CRTs. The CRT in Visual Studio 2015 provides a lot of previously missing
functions, so targeting it requires less special casing.

Differential Revision: https://reviews.llvm.org/D31798

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@299743 91177308-0d34-0410-b5e6-96231b3b80d8

src/locale.cpp

@@ -1109,13 +1109,7 @@ ctype<char>::classic_table()  _NOEXCEPT
 #elif __sun__
     return __ctype_mask;
 #elif defined(_LIBCPP_MSVCRT) || defined(__MINGW32__)
-#if _VC_CRT_MAJOR_VERSION < 14
-    // This is assumed to be safe, which is a nonsense assumption because we're
-    // going to end up dereferencing it later...
-    return _ctype+1; // internal ctype mask table defined in msvcrt.dll
-#else
     return __pctype_func();
-#endif
 #elif defined(__EMSCRIPTEN__)
     return *__ctype_b_loc();
 #elif defined(_NEWLIB_VERSION)