Do not enable pcrel-opt by default

Do not enable pcrel-opt by default

Backported from trunk.

SPEC2017 testing on p10 shows that this optimization does not have a
positive impact on performance. So we are no longer going to enable it
by default. The test cases for it needed to be updated so they always
enable it to test it.

gcc/

	* config/rs6000/rs6000-cpus.def: Take OPTION_MASK_PCREL_OPT out
	of OTHER_POWER10_MASKS so it will not be enabled by default.

gcc/testsuite/

	* gcc.target/powerpc/pcrel-opt-inc-di.c: Enable -mpcrel-opt to test it.
	* gcc.target/powerpc/pcrel-opt-ld-df.c: Enable -mpcrel-opt to test it.
	* gcc.target/powerpc/pcrel-opt-ld-di.c: Enable -mpcrel-opt to test it.
	* gcc.target/powerpc/pcrel-opt-ld-hi.c: Enable -mpcrel-opt to test it.
	* gcc.target/powerpc/pcrel-opt-ld-qi.c: Enable -mpcrel-opt to test it.
	* gcc.target/powerpc/pcrel-opt-ld-sf.c: Enable -mpcrel-opt to test it.
	* gcc.target/powerpc/pcrel-opt-ld-si.c: Enable -mpcrel-opt to test it.
	* gcc.target/powerpc/pcrel-opt-ld-vector.c: Enable -mpcrel-opt to
	test it.
	* gcc.target/powerpc/pcrel-opt-st-df.c: Enable -mpcrel-opt to test it.
	* gcc.target/powerpc/pcrel-opt-st-di.c: Enable -mpcrel-opt to test it.
	* gcc.target/powerpc/pcrel-opt-st-hi.c: Enable -mpcrel-opt to test it.
	* gcc.target/powerpc/pcrel-opt-st-qi.c: Enable -mpcrel-opt to test it.
	* gcc.target/powerpc/pcrel-opt-st-sf.c: Enable -mpcrel-opt to test it.
	* gcc.target/powerpc/pcrel-opt-st-si.c: Enable -mpcrel-opt to test it.
	* gcc.target/powerpc/pcrel-opt-st-vector.c: Enable -mpcrel-opt to
	test it.

(cherry picked from commit b7574ca6edb5ac7fab741f46d4f50ac4294c8180)