cbfstool: Fix warnings on OS X

Most hton and noth functions are already available
through the system headers we include on OS X, causing
the compiler to warn about duplicate definitions.

Change-Id: Id81852dfc028cf0c48155048c54d431436889c0e
Signed-off-by: Stefan Reinauer <reinauer@google.com>
Reviewed-on: http://review.coreboot.org/2106
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>
Reviewed-by: David Hendricks <dhendrix@chromium.org>
Tested-by: build bot (Jenkins)

util/cbfstool/common.h

@@ -22,8 +22,10 @@
 
 #include <stdint.h>
 #include "swab.h"
+#ifndef __APPLE__
 #define ntohl(x)  (host_bigendian?(x):swab32(x))
 #define htonl(x)  (host_bigendian?(x):swab32(x))
+#endif
 #define ntohll(x) (host_bigendian?(x):swab64(x))
 #define htonll(x) (host_bigendian?(x):swab64(x))