Now that the compiler accepts "-Z instrument-xray" option only when
targeting one of the supported targets, make sure to not run the
codegen tests where the compiler will fail.
Like with other compiletests, we don't have access to internals,
so simply hardcode a list of supported architectures here.
This is somewhat important because LLVM enables the pass based on
target architecture, but support by the target OS also matters.
For example, XRay attributes are processed by codegen for macOS
targets, but Apple linker fails to process relocations in XRay
data sections, so the feature as a whole is not supported there
for the time being.
