[tests] add pretty-printing test for treatment of new builtins

tests/syntax/oracle/signal.res.oracle

+[kernel] Parsing tests/syntax/signal.c (with preprocessing)
+/* Generated by Frama-C */
+#include "signal.h"
+void f(void)
+{
+  signal(10,SIG_IGN);
+  signal(12,SIG_ERR);
+  signal(31,SIG_DFL);
+  return;
+}
+
+

tests/syntax/signal.c

+#include <signal.h>
+
+void f() {
+  signal (SIGUSR1, SIG_IGN);
+  signal (SIGUSR2, SIG_ERR);
+  signal (SIGUNUSED, SIG_DFL);
+}