Make rdmd_test run verbosely for posix.mak test_rdmd target

This patch should probably be dropped before any merge of the preceding
patches, but should help to make clear that CI is indeed invoking both
dmd and ldmd2 from `rdmd_test`.

posix.mak

@@ -112,7 +112,7 @@ test_tests_extractor: $(ROOT)/tests_extractor
 	$< -i ./test/tests_extractor/iteration.d | diff - ./test/tests_extractor/iteration.d.ext
 
 test_rdmd: $(ROOT)/rdmd_test $(ROOT)/rdmd
-	$< --compiler=$(abspath $(DMD)) -m$(MODEL) --test-compilers=$(RDMD_TEST_COMPILERS)
+	$< --compiler=$(abspath $(DMD)) -m$(MODEL) -v --test-compilers=$(RDMD_TEST_COMPILERS)
 	$(DMD) $(DFLAGS) -unittest -main -run rdmd.d
 
 test: test_tests_extractor test_rdmd