Enable flate-combine.

Enable flate-combine.

Move pass_stv2 and pass_rpad after pre_reload pass_late_combine, also
define target_insn_cost to prevent post_reload pass_late_combine to
revert the optimziation did in pass_rpad.

Adjust testcases since pass_late_combine generates better code but
break scan assembly.

.i.e
Under 32-bit target, gcc used to generate broadcast from stack and
then do the real operation.
After flate_combine, they're combined into embeded broadcast
operations.

gcc/ChangeLog:

	* config/i386/i386-features.cc (ix86_rpad_gate): New function.
	* config/i386/i386-options.cc (ix86_override_options_after_change):
	Don't disable flate_combine.
	* config/i386/i386-passes.def: Move pass_stv2 and pass_rpad
	after pre_reload pas_late_combine.
	* config/i386/i386-protos.h (ix86_rpad_gate): New declare.
	* config/i386/i386.cc (ix86_insn_cost): New function.
	(TARGET_INSN_COST): Define.

gcc/testsuite/ChangeLog:

	* gcc.target/i386/avx512f-broadcast-pr87767-1.c: Adjus
	testcase.
	* gcc.target/i386/avx512f-broadcast-pr87767-5.c: Ditto.
	* gcc.target/i386/avx512f-fmadd-sf-zmm-7.c: Ditto.
	* gcc.target/i386/avx512f-fmsub-sf-zmm-7.c: Ditto.
	* gcc.target/i386/avx512f-fnmadd-sf-zmm-7.c: Ditto.
	* gcc.target/i386/avx512f-fnmsub-sf-zmm-7.c: Ditto.
	* gcc.target/i386/avx512vl-broadcast-pr87767-1.c: Ditto.
	* gcc.target/i386/avx512vl-broadcast-pr87767-5.c: Ditto.
	* gcc.target/i386/pr91333.c: Ditto.
	* gcc.target/i386/vect-strided-4.c: Ditto.