PowerPC: Change cmove function return to bool.

PowerPC: Change cmove function return to bool.

In doing the other work for adding ISA 3.1 128-bit minimum, maximum, and
conditional move support, I noticed the two functions that process conditional
moves return 'int' instead of 'bool'.  This patch changes these functions to
return 'bool'.

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-protos.h (rs6000_emit_cmove): Change return
	type to bool.
	(rs6000_emit_int_cmove): Change return type to bool.
	* config/rs6000/rs6000.c (rs6000_emit_cmove): Change return type
	to bool.
	(rs6000_emit_int_cmove): Change return type to bool.