This patch implements snprintf_l function in a way similar to the other 
functions in src/support/win32/locale_win32.cpp and locale_win32.h, 
calling upon vsnprintf for which there is a MingW correct alternative.

Note! __USE_MINGW_ANSI_STDIO is not modified in this patch. In order to 
use the __mingw version it must be defined before including the MingW 
headers.




git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@195044 91177308-0d34-0410-b5e6-96231b3b80d8