Minor tweaks to bring defs in line with MS. 

git-svn-id: https://svn.code.sf.net/p/mingw-w64/code@5981 4407c894-4637-0410-b4f5-ada5f102cad1
Support both -masm=att and -masm=intel

git-svn-id: https://svn.code.sf.net/p/mingw-w64/code@5982 4407c894-4637-0410-b4f5-ada5f102cad1