rs6000: Skip debug insns for union [PR105627]

rs6000: Skip debug insns for union [PR105627]

As PR105627 exposes, pass analyze_swaps should skip debug
insn when doing unionfind_union.  One debug insn can use
several pseudos, if we take debug insn into account, we can
union those insns defining them and generate some unexpected
unions.

Based on the assumption that it's impossible to have one
pseudo which is defined by one debug insn but is used by one
nondebug insn, we just asserts debug insn never shows up in
function union_defs.

	PR target/105627

gcc/ChangeLog:

	* config/rs6000/rs6000-p8swap.cc (union_defs): Assert def_insn can't
	be a debug insn.
	(union_uses): Skip debug use_insn.

gcc/testsuite/ChangeLog:

	* gcc.target/powerpc/pr105627.c: New test.