More on assuming GCC is greater than or equal to version 3.5.4 and that

	More on assuming GCC is greater than or equal to version 3.5.4 and that
	GCC is the only compiler to be used for MinGW.org.

	* include/userenv.h: Remove unneeded filters based on the assumptions.
	* include/usp10.h: Ditto.
	* include/uxtheme.h: Ditto.
	* include/vidcap.h: Ditto.
	* include/vmr9.h: Ditto.
	* include/vptype.h: Ditto.
	* include/w32api.h: Ditto.
	* include/winable.h: Ditto.
	* include/winbase.h: Ditto.
	* include/winber.h: Ditto.
	* include/wincon.h: Ditto.
	* include/wincrypt.h: Ditto.
	* include/windef.h: Ditto.
	* include/windns.h: Ditto.
	* include/windows.h: Ditto.
	* include/windowsx.h: Ditto.
	* include/winerror.h: Ditto.
	* include/wchar.h: Ditto.  Add GCC system_header pragma.