Pre-approved by Andrew in a separate thread, and applied to gcc SVN.  This
brings all relevant changes from the upstream libffi/x86/win32.S across to
GCC; it still needs merging back in the opposite direction, but that can now
be done simply by a wholesale replacement.

libffi/ChangeLog:

	* src/x86/win32.S (_ffi_closure_STDCALL):  New function.
	(.eh_frame):  Add FDE for it.

  Rebuilt and retested the library; no problems - not that any of the
testcases will be referring to it, anyway, but just to ensure nothing got broken.

    cheers,
      DaveK