testsuite, i386: Only check for cfi directives if supported [PR112729]

testsuite, i386: Only check for cfi directives if supported [PR112729]

gcc.target/i386/apx-interrupt-1.c and two more tests FAIL on Solaris/x86
with the native assembler.  Like Darwin as, it doesn't support cfi
directives.  Instead of adding more and more targets in every affected
test, this patch introduces a cfi effective-target keyword to check for
the prerequisite.

Tested on i386-pc-solaris2.11 (as and gas), x86_64-pc-linux-gnu, and
x86_64-apple-darwin23.1.0.

2023-11-24  Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>

	gcc/testsuite:
	PR testsuite/112729
	* lib/target-supports.exp (check_effective_target_cfi): New proc.
	* gcc.target/i386/apx-interrupt-1.c: Require cfi instead of
	skipping on *-*-darwin*.
	* gcc.target/i386/apx-push2pop2_force_drap-1.c: Likewise.
	* gcc.target/i386/apx-push2pop2-1.c: Likewise.

	gcc:
	PR testsuite/112729
	* doc/sourcebuild.texi (Effective-Target Keywords, Environment
	attributes): Document cfi.