Looking at os2emx.h, the typedef is guarded by #if defined (INCL_WINDIALOGS) so the fix is,
--- CNREZ.C.orig 2023-05-26 17:16:48.000000000 -0700
+++ CNREZ.C 2023-05-26 17:16:14.000000000 -0700
@@ -51,6 +51,7 @@
#define INCL_WINSTDCNR
#define INCL_WINSTDDLGS
#define INCL_WINWINDOWMGR
+#define INCL_WINDIALOGS
/**********************************************************************/
/*----------------------------- INCLUDES -----------------------------*/