target/119549 - fixup handling of -mno-sse4 in target attribute

target/119549 - fixup handling of -mno-sse4 in target attribute

The following fixes ix86_valid_target_attribute_inner_p to properly
handle target("no-sse4") via OPT_mno_sse4 rather than as unset OPT_msse4.
I've added asserts to ix86_handle_option that RejectNegative is honored
for both.

	PR target/119549
	* common/config/i386/i386-common.cc (ix86_handle_option):
	Assert that both OPT_msse4 and OPT_mno_sse4 are never unset.
	* config/i386/i386-options.cc (ix86_valid_target_attribute_inner_p):
	Process negated OPT_msse4 as OPT_mno_sse4.

	* gcc.target/i386/pr119549.c: New testcase.