Don't force target of modulo into a distinct register.

Don't force target of modulo into a distinct register.

The define_insns for the modulo operation currently force the target register
to a distinct reg in preparation for a possible future peephole combining
div/mod. But this can lead to cases of a needless copy being inserted. Fixed
with the following patch.

gcc/
	* config/rs6000/rs6000.md (*mod<mode>3, umod<mode>3): Add
	non-earlyclobber alternative.

gcc/testsuite/
	* gcc.target/powerpc/mod-no_copy.c: New.
	* gcc.target/powerpc/mod-peephole.c: New.