[LLDB] Remove a now redundant windows specific workaround

[mstorsjo]

Summary

vsnprintf(NULL, 0, ...) works for measuring the needed string size on all supported Windows variants; it's supported since at least MSVC 2015 (and LLVM requires a newer version than that), and works on both msvcrt.dll (since at least XP) and UCRT with MinGW.

The previous use of ifdefs was wrong as well, as __MINGW64__ only is defined for 64 bit targets, and the define without trailing underscores is never defined automatically (neither by clang nor by gcc).

[labath]

Judging by the microsoft docs, vsnprintf is avaliable at least since VS 2017 (the lowest version supported by llvm). Is it possible that we can just delete this #ifdef ?

[mstorsjo]

In D67861#1678618, @labath wrote:

Judging by the microsoft docs, vsnprintf is avaliable at least since VS 2017 (the lowest version supported by llvm). Is it possible that we can just delete this #ifdef ?

Yes, it would seem so.

With MSVC, you got an MSVC-specific version of the CRT, and with the versions of MSVC we require, it is a C99 compliant one.

With MinGW, you can link either against the UCRT (the same modern CRT as MSVC uses these days) or msvcrt.dll (the old legacy one, shipped as a part of the OS). But I checked that this use of vsnprintf(NULL, 0, ...) does seem to work with the old msvcrt.dll since at least XP (and llvm requires a much newer version of Windows anyway), so I would say that it should be safe.

[mstorsjo]

Updated the patch to simply remove the now redundant workaround.

[labath]

Awesome. Let's give that a spin.

lldb/source/Host/windows/Windows.cpp

 }
 
 int vasprintf(char **ret, const char *fmt, va_list ap) {
   char *buf;
   int len;
   size_t buflen;
   va_list ap2;
 
-#if defined(_MSC_VER) || defined(__MINGW64)
-  ap2 = ap;
-  len = _vscprintf(fmt, ap2);
-#else
   va_copy(ap2, ap);
   len = vsnprintf(NULL, 0, fmt, ap2);
-#endif
 
   if (len >= 0 &&
       (buf = (char *)malloc((buflen = (size_t)(len + 1)))) != NULL) {
     len = vsnprintf(buf, buflen, fmt, ap);
     *ret = buf;
   } else {
     *ret = NULL;
     len = -1;