Fix bug in __stosb

Patch by David Wohlferd limegreensocks@yahoo.com

1) The __buildstos macro has been removed from winnt.h
2) __buildstos has been put in the new file
mingw-w64-headers/include/psdk_inc/intrin-mac.h
3) mingw-w64-crt/intrincs/__stosb.c (and stosw.c, stosd.c, stosq.c) now
use the macro from intrin-mac.h

As a result, not only do the stos*.c files get the new code, but this
inline assembler now only exists in one place, making future maintenance
easier.

git-svn-id: https://mingw-w64.svn.sourceforge.net/svnroot/mingw-w64@5872 4407c894-4637-0410-b4f5-ada5f102cad1