Fix warnings from clang in deep_profiler directory.

deep_profiler/timeout.m:
	Mark functions that cannot return as such.

	Use don't-care variables for the I/O state in foreign_procs
	instead of an assignment in the foreign proc body.  (Both clang
	and MSVC emit spurious warnings about the latter.)

	Avoid some warnings about variables that are unused unless
	MR_DEBUG_MDPROF_SIGNAL is enabled.