The prlimit probe broke when implicit function declarations became an error

(see comment in ulimit.c about the glibc header bug), so copy prototype into
the probe too. Without this ulimit always disabled by config probe.

scripts/genconfig.sh

@@ -98,9 +98,11 @@ EOF
   echo -e '\tdepends on !TOYBOX_MUSL_NOMMU_IS_BROKEN'
 
   probesymbol TOYBOX_PRLIMIT << EOF
+    #include <sys/types.h>
     #include <sys/time.h>
     #include <sys/resource.h>
-
+    int prlimit(pid_t pid, int resource, const struct rlimit *new_limit,
+      struct rlimit *old_limit);
     int main(int argc, char *argv[]) { prlimit(0, 0, 0, 0); }
 EOF
 }