make: fix GCC warnings

@@ -304,11 +304,11 @@
                 report_dep(iflag, filename);
         }
 }
 
 void
-report_dependency(register char *name)
+report_dependency(const char *name)
 {
         register char   *filename;
         char            buffer[MAXPATHLEN+1];
         register char   *p;
         register char   *p2;