For PGO/coverage tests that don't need to build or run an actual artifact, we
can use `-Zno-profiler-runtime` to run the test even when the profiler runtime
is not available.
This adds the `only-apple`/`ignore-apple` compiletest directive, and
uses that basically everywhere instead of `only-macos`/`ignore-macos`.
Some of the updates in `run-make` are a bit redundant, as they use
`ignore-cross-compile` and won't run on iOS - but using Apple in these
is still more correct, so I've made that change anyhow.
This test was already very close to being an ordinary codegen test, except that
it needed some extra logic to set a few variables based on (target) platform
characteristics.
Now that we have support for `//@ filecheck-flags:`, we can instead set those
variables using the normal test revisions mechanism.
