Don't use __stdcall on ARM

git-svn-id: https://svn.code.sf.net/p/mingw-w64/code@6607 4407c894-4637-0410-b4f5-ada5f102cad1
Define PCONTEXT on ARM

git-svn-id: https://svn.code.sf.net/p/mingw-w64/code@6608 4407c894-4637-0410-b4f5-ada5f102cad1
Add some more ARM typedefs

git-svn-id: https://svn.code.sf.net/p/mingw-w64/code@6609 4407c894-4637-0410-b4f5-ada5f102cad1
Don't use __stdcall on ARM

git-svn-id: https://svn.code.sf.net/p/mingw-w64/code@6610 4407c894-4637-0410-b4f5-ada5f102cad1