Add -mcpu=power11 tests.

Add -mcpu=power11 tests.

This patch adds some simple tests for -mcpu=power11 support.  In order to run
these tests, you need an assembler that supports the -mpwr11 option.

2024-03-08  Michael Meissner  <meissner@linux.ibm.com>

gcc/testsuite/

	* gcc.target/powerpc/power11-1.c: New test.
	* gcc.target/powerpc/power11-2.c: Likewise.
	* gcc.target/powerpc/power11-3.c: Likewise.
	* lib/target-supports.exp (check_effective_target_power11_ok): Add new
	effective target.