meson: add cpu-features-path option for Android

Add option to include cpu-features.[ch] from a given path into the build for platforms that don't provide this out of the box. This is needed on Android.

We copy the files into the build directory instead of using them directly from the original location, for better build hygiene, and so that they are automatically included as part of CI build artifacts and such.

Need to bump meson dep for fs module.

Also see !34 (closed) for autotools variant.