aarch64: Add support for unpacked SVE FP comparisons

aarch64: Add support for unpacked SVE FP comparisons

This patch extends our vec_cmp expander to support partial FP modes.

We use a predicate mode that is narrower the operation's VPRED to govern
unpacked FP operations under flag_trapping_math, so the expansion must
handle cases where the comparison's target and governing predicates have
different modes.

While such predicates enable all of the defined part of the operation, they
are not all-true.  Their false bits contribute to the (trapping) behavior of
the operation, so we cannot have SVE_KNOWN_PTRUE.

gcc/ChangeLog:

	* config/aarch64/aarch64-sve.md (vec_cmp<mode><vpred>): Extend
	to handle partial FP modes.
	(@aarch64_pred_fcm<cmp_op><mode>): Likewise.
	(@aarch64_pred_fcmuo<mode>): Likewise.
	(*one_cmpl<mode>3): Rename to...
	(@aarch64_pred_one_cmpl<mode>_z): ... this.
	* config/aarch64/aarch64.cc (aarch64_emit_sve_fp_cond): Allow the
	target and governing predicates to have different modes.
	(aarch64_emit_sve_or_fp_conds): Likewise.
	(aarch64_emit_sve_invert_fp_cond): Likewise.
	(aarch64_expand_sve_vec_cmp_float): Likewise.

gcc/testsuite/ChangeLog:

	* gcc.target/aarch64/sve/unpacked_fcm_1.c: New test.
	* gcc.target/aarch64/sve/unpacked_fcm_2.c: Likewise.