arm: testsuite: fix arm_neon_h checks with conflicting cpu/arch

arm: testsuite: fix arm_neon_h checks with conflicting cpu/arch

GCC will complain if the -mcpu flag specifies a different architecture
to that specified in -march, but if the floating-point ABI is "soft",
then differences in the floating-point architecture features are
ignored.

However, the arm_libc_fp_abi checks whether we change the FP ABI by
adding -mfloat-abi=hard/softfp to override the defaults.  If that
fails it won't add anything.

Unfortunately arm_neon_h_ok wasn't correctly checking whether the libc
check had worked and just assumed that it would always add something
to enable FP.  That's insufficient and we need to consider this failure.
We simply mark tests as unsupported in this case.

gcc/testsuite/ChangeLog:

	* lib/target-supports.exp
	(check_effective_target_arm_neon_h_ok_nocache): Return zero if
	check_effective_target_arm_libc_fp_abi_ok reports failure.