rs6000: ROP - Emit hashst and hashchk insns on Power8 and later [PR114759]

rs6000: ROP - Emit hashst and hashchk insns on Power8 and later [PR114759]

We currently only emit the ROP-protect hash* insns for Power10, where the
insns were added to the architecture.  We want to emit them for earlier
cpus (where they operate as NOPs), so that if those older binaries are
ever executed on a Power10, then they'll be protected from ROP attacks.
Binutils accepts hashst and hashchk back to Power8, so change GCC to emit
them for Power8 and later.  This matches clang's behavior.

2024-06-19  Peter Bergner  <bergner@linux.ibm.com>

gcc/
	PR target/114759
	* config/rs6000/rs6000-logue.cc (rs6000_stack_info): Use TARGET_POWER8.
	(rs6000_emit_prologue): Likewise.
	* config/rs6000/rs6000.md (hashchk): Likewise.
	(hashst): Likewise.
	Fix whitespace.

gcc/testsuite/
	PR target/114759
	* gcc.target/powerpc/pr114759-2.c: New test.
	* lib/target-supports.exp (rop_ok): Use
	check_effective_target_has_arch_pwr8.

(cherry picked from commit a05c3d23d1e1c8d2971b123804fc7a61a3561adb)