testsuite: Correct requirements for byte-in-* testcases.

testsuite: Correct requirements for byte-in-* testcases.

commit 25ffd3d34e means we no longer define an overloaded
__builtin_byte_in_set for -m32, so the more informative
"__builtin_byte_in_set is not supported in this compiler
configuration" is not reported.

This patch changes byte-in-set-2.c to expect an implicit declaration
warning.  It also removes unnecessary target requirement for all
byte-in-*.c tests and no longer skips AIX.

gcc/testsuite/ChangeLog:

2020-10-28  David Edelsohn  <dje.gcc@gmail.com>
	    Alan Modra  <amodra@gmail.com>

	* gcc.target/powerpc/byte-in-either-range-0.c: Remove target.
	* gcc.target/powerpc/byte-in-either-range-1.c: Remove target.
	* gcc.target/powerpc/byte-in-range-0.c: Remove target.
	* gcc.target/powerpc/byte-in-range-1.c: Remove target.
	* gcc.target/powerpc/byte-in-set-0.c: Remove target.
	* gcc.target/powerpc/byte-in-set-1.c: Remove target.
	* gcc.target/powerpc/byte-in-set-2.c: Remove target. Expect
	implicit declaration warning.