Fix a couple of syntactically dangerous macros.

The live versions of the dmemdump macros had a trailing semicolon in
the expansion, which would cause them to break if used in the wrong
syntactic context (e.g. between if and else with the natural semicolon
at the call site). The conditioned-out versions of those and of
debug() itself expanded to the empty string in place of the more usual
((void)0). And SECOND_PASS_ONLY in gtkmain.c's command-line handling
should have had the standard do ... while(0) wrapper to make it
reliably a single statement.

unix/gtkmain.c

@@ -330,7 +330,7 @@ bool do_cmdline(int argc, char **argv, bool do_everything, Conf *conf)
     } else \
 	val = *++argv; \
 }
-#define SECOND_PASS_ONLY { if (!do_everything) continue; }
+#define SECOND_PASS_ONLY do { if (!do_everything) continue; } while (0)
 
     while (--argc > 0) {
 	const char *p = *++argv;