Fix phpGH-9923: Add the SIGINFO constant in pcntl for system supporting it.

Author: devnexen

ext/pcntl/pcntl.stub.php

@@ -224,6 +224,13 @@
  */
 const SIGPWR = UNKNOWN;
 #endif
+#ifdef SIGINFO
+/**
+ * @var int
+ * @cvalue LONG_CONST(SIGINFO)
+ */
+const SIGINFO = UNKNOWN;
+#endif
 #ifdef SIGSYS
 /**
  * @var int