ntdll: Mark FILE_umask with hidden visibility.

dlls/ntdll/loader.c

@@ -2847,7 +2847,6 @@ void __wine_process_init(void)
     NTSTATUS status;
     ANSI_STRING func_name;
     void (* DECLSPEC_NORETURN CDECL init_func)(void);
-    extern mode_t FILE_umask;
 
     main_exe_file = thread_init();
 

dlls/ntdll/ntdll_misc.h

@@ -232,6 +232,8 @@ static inline struct ntdll_thread_data *ntdll_get_thread_data(void)
     return (struct ntdll_thread_data *)NtCurrentTeb()->SpareBytes1;
 }
 
+extern mode_t FILE_umask DECLSPEC_HIDDEN;
+
 /* Register functions */
 
 #ifdef __i386__