[Builtin][ARM] #ifdef ARM vfp tests and cpu_model_tests

Summary:
Add in #ifdef to exclude cpu_model_test on non-X86 and  *vfp_test on ARM targets without VFP support.

This is consistent with other target-specific tests that print "Skipped" if not supported.

Reviewers: rengolin, compnerd, asbirlea

Reviewed By: compnerd

Subscribers: llvm-commits, aemerson

Differential Revision: https://reviews.llvm.org/D29882

llvm-svn: 295261