x86: Properly check saved register CFA offset

x86: Properly check saved register CFA offset

X86 prologue saves register at CFA offset.  Since its location on stack
is computed as CFA - its CFA_OFFSET, CFA_OFFSET points the end of the
saved register area on stack.  This patch updates sp_valid_at and
fp_valid_at to properly check saved register CFA offset.

gcc/

	PR target/81563
	* config/i386/i386.c (sp_valid_at): Properly check CFA offset.
	(fp_valid_at): Likewise.

gcc/testsuite/

	PR target/81563
	* gcc.target/i386/pr81563.c: New test

From-SVN: r250587