fix sh fesetround failure to clear old mode

the sh version of fesetround or'd the new rounding mode onto the
control register without clearing the old rounding mode bits, making
changes sticky. this was the root cause of multiple test failures.

src/fenv/sh/fenv.S

@@ -12,6 +12,8 @@ fegetround:
 .type   __fesetround, @function
 __fesetround:
 	sts fpscr, r0
+	mov #-4, r1
+	and r1, r0
 	or  r4, r0
 	lds r0, fpscr
 	rts