[AArch64] provide strictfp attributes in test file

A post-commit review comment on  https://reviews.llvm.org/D107452 pointed out that
https://llvm.org/docs/LangRef.html
says:
"In a function that uses the constrained intrinsics the strictfp attribute is required on all function calls."

Although there are several files across several test directories which don't follow this guidance, it is straightforward to provide this attribute.

Reviewed By: kpn

Differential Revision: https://reviews.llvm.org/D107567