correct build for rp2040 targets on macos

[kpishere]

Building for the rp2040 target would not fully compile. It presents the following error:

  Preprocessing out/src/rp2040/rpxxxx_link.ld
clang: error: no input files
make: *** [out/src/rp2040/rpxxxx_link.ld] Error 1
> _

The changes here fix the above error and a subsequent C++ standards link-error on macos environments. The scope of the change affects rpXXXX MCU targets. This is a blocking error on macos environments, I expect it isn't an issue on linux based build environments. If automated testing passes, it will have no affect on other build environments.

[kpishere]

I'm gonna pull this PR for now and add some specific OS switches. I tested on a Debian environment and this change causes issues -- even though it passes your automated testing.