m32r: fix build warning

Some m32r builds were having a warning:

  arch/m32r/include/asm/cmpxchg.h:191:3: warning: value computed is not used
  arch/m32r/include/asm/cmpxchg.h:68:3: warning: value computed is not used

Taking the idea from commit e001bbae ("ARM: cmpxchg: avoid warnings
from macro-ized cmpxchg() implementations") the m32r implementation is
changed to use a similar construct with a compound expression instead of
a typecast, which causes the compiler to not complain about an unused
result.

Link: http://lkml.kernel.org/r/1484432664-7015-1-git-send-email-sudipm.mukherjee@gmail.comSigned-off-by: Sudip Mukherjee <sudip.mukherjee@codethink.co.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/m32r/include/asm/cmpxchg.h

@@ -64,8 +64,10 @@ __xchg(unsigned long x, volatile void *ptr, int size)
 	return (tmp);
 }
 
-#define xchg(ptr, x)							\
-	((__typeof__(*(ptr)))__xchg((unsigned long)(x), (ptr), sizeof(*(ptr))))
+#define xchg(ptr, x) ({							\
+	((__typeof__(*(ptr)))__xchg((unsigned long)(x), (ptr),		\
+				    sizeof(*(ptr))));			\
+})
 
 static __always_inline unsigned long
 __xchg_local(unsigned long x, volatile void *ptr, int size)
@@ -187,9 +189,12 @@ __cmpxchg(volatile void *ptr, unsigned long old, unsigned long new, int size)
 	return old;
 }
 
-#define cmpxchg(ptr, o, n)						 \
-	((__typeof__(*(ptr))) __cmpxchg((ptr), (unsigned long)(o),	 \
-			(unsigned long)(n), sizeof(*(ptr))))
+#define cmpxchg(ptr, o, n) ({				\
+	((__typeof__(*(ptr)))				\
+		 __cmpxchg((ptr), (unsigned long)(o),	\
+			   (unsigned long)(n),		\
+			   sizeof(*(ptr))));		\
+})
 
 #include <asm-generic/cmpxchg-local.h>