x86-64: Implement libm IFUNC selectors in C

	* sysdeps/x86_64/fpu/multiarch/Makefile (libm-sysdep_routines):
	Add s_ceil-sse4_1, s_ceilf-sse4_1, s_floor-sse4_1,
	s_floorf-sse4_1, s_nearbyint-sse4_1, s_nearbyintf-sse4_1,
	s_rint-sse4_1 and s_rintf-sse4_1.
	* sysdeps/x86_64/fpu/multiarch/ifunc-sse4_1.h: New file.
	* sysdeps/x86_64/fpu/multiarch/s_ceil.c: Likewise.
	* sysdeps/x86_64/fpu/multiarch/s_ceilf.c: Likewise.
	* sysdeps/x86_64/fpu/multiarch/s_floor.c: Likewise.
	* sysdeps/x86_64/fpu/multiarch/s_floorf.c: Likewise.
	* sysdeps/x86_64/fpu/multiarch/s_nearbyint.c: Likewise.
	* sysdeps/x86_64/fpu/multiarch/s_nearbyintf.c: Likewise.
	* sysdeps/x86_64/fpu/multiarch/s_rint.c: Likewise.
	* sysdeps/x86_64/fpu/multiarch/s_rintf.c: Likewise.
	* sysdeps/x86_64/fpu/multiarch/s_ceil.S: Renamed to ...
	* sysdeps/x86_64/fpu/multiarch/s_ceil-sse4_1.S: This.  Don't
	include <machine/asm.h> nor <init-arch.h>.  Include <sysdep.h>.
	(__ceil): Removed.
	* sysdeps/x86_64/fpu/multiarch/s_ceilf.S: Renamed to ...
	* sysdeps/x86_64/fpu/multiarch/s_ceilf-sse4_1.S: This.  Don't
	include <machine/asm.h> nor <init-arch.h>.  Include <sysdep.h>.
	(__ceilf): Removed.
	* sysdeps/x86_64/fpu/multiarch/s_floor.S: Renamed to ...
	* sysdeps/x86_64/fpu/multiarch/s_floor-sse4_1.S: This.  Don't
	include <machine/asm.h> nor <init-arch.h>.  Include <sysdep.h>.
	(__floor): Removed.
	* sysdeps/x86_64/fpu/multiarch/s_floorf.S: Renamed to ...
	* sysdeps/x86_64/fpu/multiarch/s_floorf-sse4_1.S: This.  Don't
	include <machine/asm.h> nor <init-arch.h>.  Include <sysdep.h>.
	(__floorf): Removed.
	* sysdeps/x86_64/fpu/multiarch/s_nearbyint.S: Renamed to ...
	* sysdeps/x86_64/fpu/multiarch/s_nearbyint-sse4_1.S: This.  Don't
	include <machine/asm.h> nor <init-arch.h>.  Include <sysdep.h>.
	(__nearbyint): Removed.
	* sysdeps/x86_64/fpu/multiarch/s_nearbyintf.S: Renamed to ...
	* sysdeps/x86_64/fpu/multiarch/s_nearbyintf-sse4_1.S: This.  Don't
	include <machine/asm.h> nor <init-arch.h>.  Include <sysdep.h>.
	(__nearbyintf): Removed.
	* sysdeps/x86_64/fpu/multiarch/s_rint.S: Renamed to ...
	* sysdeps/x86_64/fpu/multiarch/s_rint-sse4_1.S: This.  Don't
	include <machine/asm.h> nor <init-arch.h>.  Include <sysdep.h>.
	(__rint): Removed.
	* sysdeps/x86_64/fpu/multiarch/s_rintf.S: Renamed to ...
	* sysdeps/x86_64/fpu/multiarch/s_rintf-sse4_1.S: This.  Don't
	include <machine/asm.h> nor <init-arch.h>.  Include <sysdep.h>.
	(__rintf): Removed.