sim: m32r: fix virtual environment with Linux targets

sim: m32r: fix virtual environment with Linux targets

We don't want to handle Linux syscalls when in the virtual environment,
just the user environment, so adjust the Linux traps logic to check for
that specifically (instead of just skipping the operating environment).

Also tweak some testcases to explicitly specify the environment they run
under rather than relying on the default matching their needs.  This gets
the tests passing for all m32r targets.