rs6000: Error on CPUs and ABIs that don't support the ROP protection insns [PR114759]

rs6000: Error on CPUs and ABIs that don't support the ROP protection insns [PR114759]

We currently silently ignore the -mrop-protect option for old CPUs we don't
support with the ROP hash insns, but we throw an error for unsupported ABIs.
This patch treats unsupported CPUs and ABIs similarly by throwing an error
both both.  This matches clang behavior and allows us to simplify our tests
in the code that generates our prologue and epilogue code.

2024-06-26  Peter Bergner  <bergner@linux.ibm.com>

gcc/
	PR target/114759
	* config/rs6000/rs6000.cc (rs6000_option_override_internal): Disallow
	CPUs and ABIs that do no support the ROP protection insns.
	* config/rs6000/rs6000-logue.cc (rs6000_stack_info): Remove now
	unneeded tests.
	(rs6000_emit_prologue): Likewise.
	Remove unneeded gcc_assert.
	(rs6000_emit_epilogue): Likewise.
	* config/rs6000/rs6000.md: Likewise.

gcc/testsuite/
	PR target/114759
	* gcc.target/powerpc/pr114759-3.c: New test.

(cherry picked from commit 6f2bab9b5d1ce1914c748b7dcd8638dafaa98df7)