xen: make sure that likely and unlikely convert the expression to a boolean

According to http://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html
__builtin_expect has the prototype:
    long __builtin_expect (long exp, long c)

If sizeof(exp) > sizeof(long) then this will effectively mask off the top bits
of exp, meaning that the if in "if (unlikey(x))" will see the masked version,
which might be false when true was expected, likely has the same issue.

This is mostly likely to affect x86_32 and arm32 builds.  x86_32 is not
present on 4.3 onwards and a quick grep of current staging shows that all the
existing arm32  uses of both likely and unlikely already pass a boolean. I
noticed this with an as yet unposted patch which did not have this property.

Also the defintion of likely might not have had the expected affect for cases
where a true value > 1 might be passed.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Cc: Keir Fraser <keir@xen.org>
Cc: Tim Deegan <tim@xen.org>

xen/include/xen/compiler.h

@@ -7,8 +7,8 @@
 
 #define barrier()     __asm__ __volatile__("": : :"memory")
 
-#define likely(x)     __builtin_expect((x),1)
-#define unlikely(x)   __builtin_expect((x),0)
+#define likely(x)     __builtin_expect(!!(x),1)
+#define unlikely(x)   __builtin_expect(!!(x),0)
 
 #define inline        __inline__
 #define always_inline __inline__ __attribute__ ((always_inline))