Fix runtime errors when built with UBSan

nopen.c:37:15: runtime error: left shift of 1 by 31 places cannot be
 represented in type 'int'
nopen.c:39:18: runtime error: left shift of 1 by 31 places cannot be
 represented in type 'int'
userdat.c:251:111: runtime error: left shift of 1 by 31 places cannot be
 represented in type 'int'

There are lot of 1<<31 macro definitions in this repo, so I'm expecting a
lot more of this type of fix to be required to make UBSan happy.

src/xpdev/filewrap.h

@@ -99,7 +99,7 @@
 		#define O_BINARY	0		/* all files in binary mode on Unix */
 		#endif
 		#undef	O_DENYNONE
-		#define O_DENYNONE  (1<<31)	/* req'd for Baja/nopen compatibility */
+		#define O_DENYNONE  (1U<<31)	/* req'd for Baja/nopen compatibility */
 
 		#define SH_DENYNO	2          /* no locks */
 		#ifdef F_SANEWRLCKNO