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'.

gcc/
2020-09-10  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.