subreg: Fix PR94123, SVN r273240 causes gcc.target/powerpc/pr87507.c to fail

subreg: Fix PR94123, SVN r273240 causes gcc.target/powerpc/pr87507.c to fail

Segher's patch that added -fsplit-wide-types-early and enabled by default
for rs6000, caused pr87507.c to FAIL because when running lower-subreg
earlier, we don't see any pseudo-to-pseudo copies of our wide type,
which are created by combine, therefore, we skip decomposing our TImode
accesses.  The fix here is just to always run the third pass of lower-subreg
instead of disabling it if we ran the second pass.

2020-04-01  Peter Bergner  <bergner@linux.ibm.com>

	PR rtl-optimization/94123
	* lower-subreg.c (pass_lower_subreg3::gate): Remove test for
	flag_split_wide_types_early.