Matthew Dempsky: In libc++'s <locale>, there's already dependence on an snprintf_l

Matthew Dempsky:  In libc++'s <locale>, there's already dependence on an snprintf_l
implementation and all of the char buffers readily have their
allocated size available, so we can easily use snprintf_l instead of
sprintf_l.

This avoids OpenBSD's linker warnings against using sprintf and
vsprintf.
Howard:  Please consider a patch for CREDITS.TXT

llvm-svn: 185457