Fix PowerPC ICE due to secondary_reload ignoring reload replacements

Fix PowerPC ICE due to secondary_reload ignoring reload replacements

The reason for this PR is that insns emitted by secondary reload
patterns are being generated without taking into account other reloads
that may have occurred.  We run into this problem when an insn has a
pseudo that doesn't get a hard reg, and the pseudo is used in a way
that requires a secondary reload.  In this case the secondary reload
is needed due to gcc generating a 64-bit gpr load from memory insn
with an address offset not a multiple of 4.

	PR target/67378
	* config/rs6000/rs6000.c (rs6000_secondary_reload_gpr): Find
	reload replacement for PRE_MODIFY address reg.

From-SVN: r227573