The wrapper around `arm-none-eabi-gdb` was not passing through
the command line arguments. This would cause build systems that
attempted to determine the gdb version to hang.
Match the other wrapper by adding `"$@"`, and using `exec` to
call the unwrapped process.
Our gcc-arm-embedded expressions download binaries instead of
building from source. Let's add the appropriate `sourceProvenance`
for this kind of thing.
