Fix up plafform testes in check headers. After a resent GCC change
the previously submitted BMI/BMI2 intrinsic test started to fail
with a warning/error.

[gcc/testsuite]

2017-07-19  Steven Munroe  <munroesj@gcc.gnu.org>

	* gcc.target/powerpc/bmi-check.h (main): Skip unless
	__BUILTIN_CPU_SUPPORTS__ defined.
	* gcc.target/powerpc/bmi2-check.h (main): Skip unless
	__BUILTIN_CPU_SUPPORTS__ defined.

From-SVN: r250362