gas: sframe: ignore .cfi_offset for RA selectively

gas: sframe: ignore .cfi_offset for RA selectively

For ABIs not tracking RA (e.g., AMD64), the return address is expected
to be in a specific location (usually a fixed offset from CFA on stack).
Explicit manourvering to a different offset may be non-representable in
SFrame, and should not be simply ignored.

Although such patterns are not usually seen in the wild, it is more
correct to catch them if at all they manifest.

Reviewed-by: Jens Remus <jremus@linux.ibm.com>
gas/
	* gen-sframe.c (sframe_xlate_do_offset): Do not ignore
	.cfi_offset for RA all the time.