Suppress compiler warnings about "value computed is not used".

The recent patch to remove gcc 4.6 warnings created some new ones, at
least on my rather old gcc version.  Try to make everybody happy by
casting to "void" when we just want to discard the result.

src/interfaces/ecpg/ecpglib/descriptor.c

@@ -775,16 +775,16 @@ ECPGdescribe(int line, int compat, bool input, const char *connection_name, cons
 
 		/* rest of variable parameters */
 		ptr = va_arg(args, void *);
-		va_arg(args, long);		/* skip args */
-		va_arg(args, long);
-		va_arg(args, long);
+		(void) va_arg(args, long);		/* skip args */
+		(void) va_arg(args, long);
+		(void) va_arg(args, long);
 
 		/* variable indicator */
-		va_arg(args, enum ECPGttype);
-		va_arg(args, void *);	/* skip args */
-		va_arg(args, long);
-		va_arg(args, long);
-		va_arg(args, long);
+		(void) va_arg(args, enum ECPGttype);
+		(void) va_arg(args, void *);	/* skip args */
+		(void) va_arg(args, long);
+		(void) va_arg(args, long);
+		(void) va_arg(args, long);
 
 		switch (type)
 		{