builtins-3.c: Move vec_neg builtin tests to Power 8 test file.

builtins-3.c: Move vec_neg builtin tests to Power 8 test file.

gcc/testsuite/ChangeLog:

2018-02-26  Carl Love  <cel@us.ibm.com>
	* gcc.target/powerpc/builtins-3.c: Move vec_neg builtin tests to
	Power 8 test file.
	* gcc.target/powerpc/builtins-3-p8.c: Add vec_neg builtin tests.
	* gcc.target/powerpc/fold-vec-neg-char.c(dg-options): Add -mcpu=power8.
	* gcc.target/powerpc/fold-vec-neg-floatdouble.c(dg-options): Add
	-mcpu=power8.
	* gcc.target/powerpc/fold-vec-neg-int.c(dg-options): Remove file.
	* gcc.target/powerpc/fold-vec-neg-short.c(dg-options): Add
	-mcpu=power8.

From-SVN: r258006