rs6000: Expand fmod and remainder when built with fast-math [PR97142]

rs6000: Expand fmod and remainder when built with fast-math [PR97142]

fmod/fmodf and remainder/remainderf could be expanded instead of library
call when fast-math build, which is much faster.

fmodf:
     fdivs   f0,f1,f2
     friz    f0,f0
     fnmsubs f1,f2,f0,f1

remainderf:
     fdivs   f0,f1,f2
     frin    f0,f0
     fnmsubs f1,f2,f0,f1

SPEC2017 Ofast P8LE: 511.povray_r +1.14%,  526.blender_r +1.72%

gcc/ChangeLog:

2021-09-07  Xionghu Luo  <luoxhu@linux.ibm.com>

	PR target/97142
	* config/rs6000/rs6000.md (fmod<mode>3): New define_expand.
	(remainder<mode>3): Likewise.

gcc/testsuite/ChangeLog:

2021-09-07  Xionghu Luo  <luoxhu@linux.ibm.com>

	PR target/97142
	* gcc.target/powerpc/pr97142.c: New test.

	(cherry-picked from 546ecb0054af302acf0839c7f3eb78598f8c0672)