Fix incorrect use of bool

NSUnLinkModule() doesn't take a bool as second argument but one of set
of specific constants.  The numeric values are the same in this case,
but clean it up while we're cleaning up bool use elsewhere.
Reviewed-by: Michael Paquier <michael.paquier@gmail.com>

src/backend/port/dynloader/darwin.c

@@ -69,7 +69,7 @@ pg_dlopen(char *filename)
 void
 pg_dlclose(void *handle)
 {
-	NSUnLinkModule(handle, FALSE);
+	NSUnLinkModule(handle, NSUNLINKMODULE_OPTION_NONE);
 }
 
 PGFunction