PowerPC: Rename functions for min, max, cmove.

PowerPC: Rename functions for min, max, cmove.

This patch renames the functions that generate the ISA 3.0 C minimum, C
maximum, and conditional move instructions to use a better name than just using
a _p9 suffix.  Because the functions can fail, the names use "maybe_emit"
instead of "generate_" in the name.

I have built compilers on a little endian power9 Linux system with all 4
patches applied.  I did bootstrap builds and ran the testsuite, with no
regressions.  Previous versions of the patch was also tested on a little endian
power8 Linux system.  I would like to check this patch into the master
branch for GCC 11.  At this time, I do not anticipate needing to backport these
changes to GCC 10.3.

gcc/
2020-09-01  Michael Meissner  <meissner@linux.ibm.com>

	* config/rs6000/rs6000.c (rs6000_emit_p9_fp_minmax): Rename to
	maybe_emit_fp_c_minmax.
	(maybe_emit_fp_c_minmax): Rename rs6000_emit_p9_fp_minmax.  Return
	bool instead of int.
	(rs6000_emit_p9_fp_cmove): Rename to maybe_emit_fp_cmove.
	(maybe_emit_fp_cmove): Rename rs6000_emit_p9_fp_cmove.  Return
	bool instead of int.
	(have_compare_and_set_mask): New helper function.
	(rs6000_emit_cmove): Rework support of ISA 3.0 functions to
	generate "C" minimum, "C" maximum, and conditional move
	instructions for scalar floating point.