modula-2: Amend the handling of failed select() calls in RTint [PR108835].

modula-2: Amend the handling of failed select() calls in RTint [PR108835].

When we make a select() that fails, there is an attempt to (a) diagnose
why and (b) make a fallback.  These actions are causing some tests to
hang on some Darwin versions, this is because the first action that is
tried to assist in diagnosis/fallback handling is to replace the set
timeout with NIL (which causes select to wait forever, modulo other
reasons it might complete).

To fix this, call select with a zero timeout when checking for error
conditions.  Also, as we check the possible failure conditions, if we
find a change that succeeds, then stop looking for errors.

Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
	PR testsuite/108835

gcc/m2/ChangeLog:

	* gm2-libs/RTint.mod: Do not use NIL timeout setting on select,
	test failures sequentially, finishing on the first success.