support: Invent verbose_printf macro

Make it easier for tests to emit progress messages only when --verbose is
specified.

* support/test-driver.h: Add verbose_printf macro.

ChangeLog

@@ -1,5 +1,7 @@
 2019-06-20  Mike Crowe  <mac@mcrowe.com>
 
+	* support/test-driver.h: Add verbose_printf macro.
+
 	* support/xtime.h: Add xclock_now() helper function.
 
 2019-06-20  Dmitry V. Levin  <ldv@altlinux.org>

support/test-driver.h

@@ -69,6 +69,14 @@ extern const char *test_dir;
    tests.  */
 extern unsigned int test_verbose;
 
+/* Output that is only emitted if at least one --verbose argument was
+   specified. */
+#define verbose_printf(...)                      \
+  do {                                           \
+    if (test_verbose > 0)                        \
+      printf (__VA_ARGS__);                      \
+  } while (0);
+
 int support_test_main (int argc, char **argv, const struct test_config *);
 
 __END_DECLS