noux_fork: use pause() instead of endless loop

At least with base-hw, the endless loop at the end of the fork
parent slows execution of the fork child dramatically. Using
libc function pause() is a cleaner solution anyways.

ref #964

ports/src/test/noux_fork/test.cc

@@ -37,6 +37,6 @@ int main(int, char **)
 		printf("pid %d: parent i = %d\n", getpid(), i++);
 	}
 
-	for (;;);
+	pause();
 	return 0;
 }