* intrincs/membarrier.c: Include <intrin.h>.  Add "for x86 only"
	comment, as in other x86-only files.  Drop gratuitous declaration.


git-svn-id: https://mingw-w64.svn.sourceforge.net/svnroot/mingw-w64@5727 4407c894-4637-0410-b4f5-ada5f102cad1