Don't align _CONTEXT on ARM as the toolchain isn't ready for this yet

git-svn-id: svn+ssh://svn.code.sf.net/p/mingw-w64/code/trunk@6619 4407c894-4637-0410-b4f5-ada5f102cad1
_chgsignl: Add ARM implementation

git-svn-id: svn+ssh://svn.code.sf.net/p/mingw-w64/code/trunk@6620 4407c894-4637-0410-b4f5-ada5f102cad1