s390: pass endianness info to sparse

s390 is big-endian only but sparse assumes the same endianness
as the building machine.
This is problematic for code which expect __BYTE_ORDER__ being
correctly predefined by the compiler which sparse can then
pre-process differently from what gcc would, depending on the
building machine endianness.

Fix this by letting sparse know about the architecture endianness.
Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/Makefile

@@ -21,7 +21,7 @@ KBUILD_CFLAGS	+= -m64
 KBUILD_AFLAGS	+= -m64
 UTS_MACHINE	:= s390x
 STACK_SIZE	:= 16384
-CHECKFLAGS	+= -D__s390__ -D__s390x__
+CHECKFLAGS	+= -D__s390__ -D__s390x__ -mbig-endian
 
 export LD_BFD