[PATCH] uml: better diagnostics for broken configs

Produce a compile-time error if both MODE_SKAS and MODE_TT are disabled.
Signed-off-by: NJeff Dike <jdike@addtoit.com>
Cc: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

arch/um/include/choose-mode.h

@@ -23,6 +23,9 @@ static inline void *__choose_mode(void *tt, void *skas) {
 
 #elif defined(UML_CONFIG_MODE_TT)
 #define CHOOSE_MODE(tt, skas) (tt)
+
+#else
+#error CONFIG_MODE_SKAS and CONFIG_MODE_TT are both disabled
 #endif
 
 #define CHOOSE_MODE_PROC(tt, skas, args...) \