xen/arm32: __cmpxchg_mb should be marked always_inline

Currently __cmpxchg_mb is only marked inline. The compiler can decide to not
inline this function. In this case, the call to __cmpxchg will be inlined
but not optimised. This will result linking failure because of __bad_cmpxchg.

Caught by clang 3.5.

Signed-off-by: Julien Grall <julien.grall@linaro.org>
Acked-by: Ian Campbell <ian.campbell@citrix.com>

xen/include/asm-arm/arm32/cmpxchg.h

@@ -112,8 +112,9 @@ static always_inline unsigned long __cmpxchg(
 	return oldval;
 }
 
-static inline unsigned long __cmpxchg_mb(volatile void *ptr, unsigned long old,
-					 unsigned long new, int size)
+static always_inline unsigned long __cmpxchg_mb(volatile void *ptr,
+                                                unsigned long old,
+                                                unsigned long new, int size)
 {
 	unsigned long ret;