re PR target/15184 (Direct access to byte inside word not working with -march=pentiumpro)

	PR target/15184
	* combine.c (try_combine): If I0 is a memory load and I3 a store
	to a related address, increase the "goodness" of doing a 4-insn
	combination with I0-I3.
	(make_field_assignment): Handle SUBREGs in the ior+and case.

	PR target/15184
	* gcc.target/i386/pr15184-1.c: New test.
	* gcc.target/i386/pr15184-2.c: New test.

From-SVN: r220249