maint: pacify gcc -flto -Wmaybe-uninitialized

* gl/lib/xdectoint.c (__xnumtoint): Tell gcc that ‘error’
does not return here.
* gl/modules/xdectoint (Depends-on): Add stdbool, verify.

gl/lib/xdectoint.c

@@ -21,10 +21,12 @@
 
 #include <errno.h>
 #include <inttypes.h>
+#include <stdbool.h>
 #include <stdlib.h>
 
 #include "error.h"
 #include "quote.h"
+#include "verify.h"
 #include "xstrtol.h"
 
 /* Parse numeric string N_STR of base BASE, and return the value.
@@ -68,6 +70,7 @@ __xnumtoint (char const *n_str, int base, __xdectoint_t min, __xdectoint_t max,
       /* EINVAL error message is redundant in this context.  */
       error (err_exit ? err_exit : EXIT_FAILURE, errno == EINVAL ? 0 : errno,
              "%s: %s", err, quote (n_str));
+      assume (false);
     }
 
   return tnum;

gl/modules/xdectoint

@@ -11,6 +11,8 @@ Depends-on:
 error
 errno
 quote
+stdbool
+verify
 xstrtoimax
 xstrtoumax