Fixed unused-parameters/unused-variables warnings

Added a ARG_UNUSED macro in utils/magic.h, which
produces a simple cast to void to silence the warnings.
The reasons this is used as opposed to an attribute is
that most compilers should support this.
Besides this, the macro can be easily searched for in
the future to potentially remove (where possible) the
unused parameters.

extract/ExtTech.c

@@ -18,9 +18,6 @@
  *     *********************************************************************
  */
 
-#ifndef lint
-static char sccsid[] = "@(#)ExtTech.c	4.8 MAGIC (Berkeley) 10/26/85";
-#endif  /* not lint */
 
 #include <stdio.h>
 #include <stdlib.h>		/* for strtod() */
@@ -543,7 +540,6 @@ int
 ExtGetDiffTypesMask(mask)
     TileTypeBitMask *mask;
 {
-    TileType ttype;
 
     if (ExtCurStyle == NULL) return 1;
 
@@ -808,7 +804,6 @@ ExtStyle *
 extTechStyleAlloc()
 {
     ExtStyle *style;
-    TileType r;
 
     style = (ExtStyle *) mallocMagic(sizeof (ExtStyle));
     return style;
@@ -1112,7 +1107,6 @@ void
 ExtTechInit()
 {
     ExtKeep *style;
-    int r;
 
     /* Delete everything in ExtCurStyle */
 
@@ -1177,7 +1171,6 @@ ExtTechSimpleAreaCap(argc, argv)
     TileType s, t;
     TileTypeBitMask types, subtypes, shields;
     CapValue capVal;
-    float multVal;
     int plane1, plane2, plane3, pnum1, pnum2, pnum3;
     PlaneMask pshield;
 
@@ -1969,7 +1962,8 @@ ExtTechLine(sectionName, argc, argv)
     int argc;
     char *argv[];
 {
-    int n, l, i, j, size, val, p1, p2, p3, nterm, iterm, class;
+    ARG_UNUSED(sectionName);
+    int n, l, i, j, val, p1, p2, p3, nterm, iterm, class;
     PlaneMask pshield, pov;
     CapValue capVal, gscap, gccap;
     ResValue resVal;
@@ -1983,7 +1977,6 @@ ExtTechLine(sectionName, argc, argv)
     ExtKeep *es, *newStyle;
     ParamList *subcktParams, *newParam;
     ExtDevice *devptr;
-    int refcnt;
     int offset;
     double dhalo;
     double doffset;
@@ -3479,7 +3472,6 @@ diffplane:
 void
 ExtTechFinal()
 {
-    ExtStyle *es;
     TileType s, t;
 
     /* Create a "default" style if there isn't one */