9pfsd: fix release build with old gcc

Being able to recognize that "par" is reliably initialized on the 1st
loop iteration requires not overly old compilers.

Fixes: 7809132b1a ("tools/xen-9pfsd: add 9pfs response generation support")
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
master commit: 984cb316cb
master date: 2024-08-02 08:44:22 +0200

tools/9pfsd/io.c

@@ -196,7 +196,7 @@ static void fill_buffer_at(void **data, const char *fmt, ...);
 static void vfill_buffer_at(void **data, const char *fmt, va_list ap)
 {
     const char *f;
-    const void *par;
+    const void *par = NULL; /* old gcc */
     const char *str_val;
     const struct p9_qid *qid;
     const struct p9_stat *stat;