[PR89221] Continue to default to '--disable-frame-pointer' for x86 GNU systems

[PR89221] Continue to default to '--disable-frame-pointer' for x86 GNU systems

The recent trunk r270914 for PR89221 "--enable-frame-pointer does not work as
intended" fixed a scripting defect in the x86 '--enable-frame-pointer'
handling.

This has the side effect that, for example, for '--target=i686-gnu' this is now
enabled by default: 'USE_IX86_FRAME_POINTER=1' is added to 'tm_defines'.  Given
that it's highly unlikely that anyone would now suddenly want
'--enable-frame-pointer' as the default for any kind of GNU system, I'm
changing the default back for GNU systems, to match that of a 'target_os' of
'linux* | darwin[8912]*'.

	gcc/
	PR target/89221
	* configure.ac (--enable-frame-pointer): Disable by default for
	GNU systems.
	* configure: Regenerate.

From-SVN: r271028