[libc++] Clean up MSVC support

[smeenai]

Summary

Visual Studio 2013 (CRT version 12) added support for many C99 long long
and long double functions. Visual Studio 2015 (CRT version 14) increased
C99 and C11 compliance further. Since we don't support Visual Studio
versions older than 2013, we can considerably clean up the support
header.

[EricWF]

This LGTM but I'll let @compnerd give it the final OK, since I've never built libc++ on windows.

include/support/win32/support.h

48

Maybe fold these to #if's into #if defined(_VC_CRT_MAJOR_VERSION) && _VC_CRT_MAJOR_VERSION < 14.

[smeenai]

include/support/win32/support.h

48

Good idea.

[smeenai]

Simpliying conditional per EricWF's suggestion

[compnerd]

SVN r280988

include/support/win32/support.h

 #include <wchar.h> // mbstate_t
 #include <cstdarg> // va_ macros
 // "builtins" not implemented here for Clang or GCC as they provide
 // implementations. Assuming required for elsewhere else, certainly MSVC.
 #if defined(_LIBCPP_MSVC)
 #include <intrin.h>
 #endif
 #if defined(_LIBCPP_MSVCRT)
-#include <xlocinfo.h>
+#include <crtversion.h>
 #endif
 #define swprintf _snwprintf
 #define vswprintf _vsnwprintf
 
 #ifndef NOMINMAX
 #define NOMINMAX
 #endif
 
 // The mingw headers already define these as static.
 #ifndef __MINGW32__
 extern "C" {
 
 int vasprintf(char **sptr, const char *__restrict fmt, va_list ap);
 int asprintf(char **sptr, const char *__restrict fmt, ...);
 size_t mbsnrtowcs(wchar_t *__restrict dst, const char **__restrict src,
                   size_t nmc, size_t len, mbstate_t *__restrict ps);
 size_t wcsnrtombs(char *__restrict dst, const wchar_t **__restrict src,
                   size_t nwc, size_t len, mbstate_t *__restrict ps);
 }
 #endif // __MINGW32__
 
-#if defined(_LIBCPP_MSVCRT)
+#if defined(_VC_CRT_MAJOR_VERSION) && _VC_CRT_MAJOR_VERSION < 14
 #define snprintf _snprintf
-#define atoll _atoi64
-#define strtoll _strtoi64
-#define strtoull _strtoui64
-#define wcstoll _wcstoi64
-#define wcstoull _wcstoui64
-_LIBCPP_ALWAYS_INLINE float strtof(const char *nptr, char **endptr)
-{
-  return _Stof(nptr, endptr, 0);
-}
-_LIBCPP_ALWAYS_INLINE double strtod(const char *nptr, char **endptr)
-{
-  return _Stod(nptr, endptr, 0);
-}
-_LIBCPP_ALWAYS_INLINE long double strtold(const char *nptr, char **endptr)
-{
-  return _Stold(nptr, endptr, 0);
-}
-
 #define _Exit _exit
 #endif
 
 #if defined(_LIBCPP_MSVC)
 
 // Bit builtin's make these assumptions when calling _BitScanForward/Reverse
 // etc. These assumptions are expected to be true for Win32/Win64 which this
 // file supports.