[asan] Loosen test for upcoming ppc64 change

This test casts 0x4 to a function pointer and calls it. Unfortunately, the
faulting address may not exactly be 0x4 on PPC64 ELFv1 systems. The LLVM PPC
backend used to always generate the loads "in order", so we'd fault at 0x4
anyway. However, at upcoming change to loosen that ordering, and we'll pick a
different order on some targets. As a result, as explained in the comment, we
need to allow for certain nearby addresses as well.

llvm-svn: 226202