test-many-klibcs: Apply timeout to test programs

Sometimes bugs cause test programs to run indefinitely.  Use timeout
to kill them after 30 seconds, which should be long enough for any
one test program to complete.
diff --git a/test-many-klibcs b/test-many-klibcs
index 9f430fb..0f45de0 100755
--- a/test-many-klibcs
+++ b/test-many-klibcs
@@ -79,7 +79,7 @@
 }
 
 run_built() {
-    $(qemu_prefix) "$@"
+    timeout 30 $(qemu_prefix) "$@"
 }
 
 patch_interp() {