Add a test for --quiet in test harness.

Author: SimonSapin

src/test/run-make/test-harness/Makefile

@@ -5,3 +5,5 @@ all:
 	$(RUSTC) --test test-ignore-cfg.rs --cfg ignorecfg
 	$(call RUN,test-ignore-cfg) | grep 'shouldnotignore ... ok'
 	$(call RUN,test-ignore-cfg) | grep 'shouldignore ... ignored'
+	$(call RUN,test-ignore-cfg --quiet) | grep "^i\.$$"
+	$(call RUN,test-ignore-cfg --quiet) | grep -v 'should'