[iguana] Run the tests when cross compiled

Summary: This leverages the emulator to run the test on different platforms, and cmake's generator expression to get the full path to the binary, including the suffix if needed (iguana.exe on windows).

Test Plan:

ninja check

Run the aarch64 and arm cross builds.

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D16853