vect: Add support for fmax and fmin reductions

vect: Add support for fmax and fmin reductions

This patch adds support for reductions involving calls to fmax*()
and fmin*(), without the -ffast-math flags that allow them to be
converted to MAX_EXPR and MIN_EXPR.

gcc/
	* doc/md.texi (reduc_fmin_scal_@var{m}): Document.
	(reduc_fmax_scal_@var{m}): Likewise.
	* optabs.def (reduc_fmax_scal_optab): New optab.
	(reduc_fmin_scal_optab): Likewise
	* internal-fn.def (REDUC_FMAX, REDUC_FMIN): New functions.
	* tree-vect-loop.c (reduction_fn_for_scalar_code): Handle
	CASE_CFN_FMAX and CASE_CFN_FMIN.
	(neutral_op_for_reduction): Likewise.
	(needs_fold_left_reduction_p): Likewise.
	* config/aarch64/iterators.md (FMAXMINV): New iterator.
	(fmaxmin): Handle UNSPEC_FMAXNMV and UNSPEC_FMINNMV.
	* config/aarch64/aarch64-simd.md (reduc_<optab>_scal_<mode>): Fix
	unspec mode.
	(reduc_<fmaxmin>_scal_<mode>): New pattern.
	* config/aarch64/aarch64-sve.md (reduc_<fmaxmin>_scal_<mode>):
	Likewise.

gcc/testsuite/
	* gcc.dg/vect/vect-fmax-1.c: New test.
	* gcc.dg/vect/vect-fmax-2.c: Likewise.
	* gcc.dg/vect/vect-fmax-3.c: Likewise.
	* gcc.dg/vect/vect-fmin-1.c: New test.
	* gcc.dg/vect/vect-fmin-2.c: Likewise.
	* gcc.dg/vect/vect-fmin-3.c: Likewise.
	* gcc.target/aarch64/fmaxnm_1.c: Likewise.
	* gcc.target/aarch64/fmaxnm_2.c: Likewise.
	* gcc.target/aarch64/fminnm_1.c: Likewise.
	* gcc.target/aarch64/fminnm_2.c: Likewise.
	* gcc.target/aarch64/sve/fmaxnm_2.c: Likewise.
	* gcc.target/aarch64/sve/fmaxnm_3.c: Likewise.
	* gcc.target/aarch64/sve/fminnm_2.c: Likewise.
	* gcc.target/aarch64/sve/fminnm_3.c: Likewise.