rs6000: Implemented f[min/max]_optab by xs[min/max]dp

rs6000: Implemented f[min/max]_optab by xs[min/max]dp

gcc/
	PR target/103605
	* config/rs6000/rs6000-builtin.cc (rs6000_gimple_fold_builtin): Gimple
	fold RS6000_BIF_XSMINDP and RS6000_BIF_XSMAXDP when fast-math is set.
	* config/rs6000/rs6000.md (FMINMAX): New int iterator.
	(minmax_op): New int attribute.
	(UNSPEC_FMAX, UNSPEC_FMIN): New unspecs.
	(f<minmax_op><mode>3): New pattern by UNSPEC_FMAX and UNSPEC_FMIN.
	* config/rs6000/rs6000-builtins.def (__builtin_vsx_xsmaxdp): Set
	pattern to fmaxdf3.
	(__builtin_vsx_xsmindp): Set pattern to fmindf3.

gcc/testsuite/
	PR target/103605
	* gcc.target/powerpc/pr103605.h: New.
	* gcc.target/powerpc/pr103605-1.c: New.
	* gcc.target/powerpc/pr103605-2.c: New.