Fix -Wundef warnings for HAVE_RB_EXT_RACTOR_SAFE

* See [Feature #17752]

ext/cgi/escape/escape.c

@@ -388,7 +388,7 @@ cgiesc_unescape(int argc, VALUE *argv, VALUE self)
 void
 Init_escape(void)
 {
-#if HAVE_RB_EXT_RACTOR_SAFE
+#ifdef HAVE_RB_EXT_RACTOR_SAFE
     rb_ext_ractor_safe(true);
 #endif
 

ext/monitor/monitor.c

@@ -203,7 +203,7 @@ monitor_synchronize(VALUE monitor)
 void
 Init_monitor(void)
 {
-#if HAVE_RB_EXT_RACTOR_SAFE
+#ifdef HAVE_RB_EXT_RACTOR_SAFE
     rb_ext_ractor_safe(true);
 #endif
 

ext/racc/cparse/cparse.c

@@ -819,7 +819,7 @@ reduce0(RB_BLOCK_CALL_FUNC_ARGLIST(_, data))
 void
 Init_cparse(void)
 {
-#if HAVE_RB_EXT_RACTOR_SAFE
+#ifdef HAVE_RB_EXT_RACTOR_SAFE
     rb_ext_ractor_safe(true);
 #endif
 

ext/zlib/zlib.c

@@ -4564,7 +4564,7 @@ zlib_gunzip_run(VALUE arg)
 void
 Init_zlib(void)
 {
-#if HAVE_RB_EXT_RACTOR_SAFE
+#ifdef HAVE_RB_EXT_RACTOR_SAFE
     rb_ext_ractor_safe(true);
 #endif