Remove copysign post_reload splitter for scalar modes.

Remove copysign post_reload splitter for scalar modes.

It can generate better code just like avx512dq-abs-copysign-1.c
shows.

gcc/ChangeLog:

	* config/i386/i386-expand.c (ix86_expand_copysign): Expand
	right into ANDNOT + AND + IOR, using paradoxical subregs.
	(ix86_split_copysign_const): Remove.
	(ix86_split_copysign_var): Ditto.
	* config/i386/i386-protos.h (ix86_split_copysign_const): Dotto.
	(ix86_split_copysign_var): Ditto.
	* config/i386/i386.md (@copysign<mode>3_const): Ditto.
	(@copysign<mode>3_var): Ditto.

gcc/testsuite/ChangeLog:

	* gcc.target/i386/avx512dq-abs-copysign-1.c: Adjust testcase.
	* gcc.target/i386/avx512vl-abs-copysign-1.c: Adjust testcase.