Fixes for GCC 15.

Doesn't include C23 changes, since those would be more extensive.

--- pccts/sorcerer/gen.c	2001-06-03 18:37:29.000000000 +0100
+++ pccts/sorcerer/gen.c	2025-07-03 19:09:34.322392102 +0100
@@ -56,7 +56,7 @@
 #include "sym.h"
 #include "proto.h"
 
-static outfile = -1;
+static int outfile = -1;
 static char *current_rule;
 static ListNode *labels_for_func = NULL;
 static AST *whichRule;
--- pccts/support/genmk/genmk.c	2000-12-04 16:05:21.000000000 +0000
+++ pccts/support/genmk/genmk.c	2025-07-03 19:10:58.385643319 +0100
@@ -94,6 +94,7 @@
 
 #ifdef __STDC__
 static void ProcessArgs(int, char **, Opt *);
+static void pclasses(char **classes, int n, char *suffix);
 #else
 static void ProcessArgs();
 #endif
@@ -965,6 +966,7 @@
 	}
 }
 
+void
 #ifdef __STDC__
 pclasses(char **classes, int n, char *suffix)
 #else