rs6000: apply -mbig option to vec-extract[hl] testcases conditionally.

rs6000: apply -mbig option to vec-extract[hl] testcases conditionally.

gcc/testsuite/ChangeLog

2020-06-19  David Edelsohn  <dje.gcc@gmail.com>

	* gcc.target/powerpc/vec-extracth-be-0.c: Apply -mbig
	conditionally for powerpc64le*-*-*.
	* gcc.target/powerpc/vec-extracth-be-1.c: Same.
	* gcc.target/powerpc/vec-extracth-be-2.c: Same.
	* gcc.target/powerpc/vec-extracth-be-3.c: Same.
	* gcc.target/powerpc/vec-extractl-be-0.c: Same.
	* gcc.target/powerpc/vec-extractl-be-1.c: Same.
	* gcc.target/powerpc/vec-extractl-be-2.c: Same.
	* gcc.target/powerpc/vec-extractl-be-3.c: Same.