/usr/lib/gcc-cross/s390x-linux-gnu/8/include/ is in libobjc-8-dev-s390x-cross 8-20180414-1ubuntu2cross1.
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/usr/lib/gcc-cross/s390x-linux-gnu/8/include/objc/
/usr/lib/gcc-cross/s390x-linux-gnu/8/include/objc/NXConstStr.h
/usr/lib/gcc-cross/s390x-linux-gnu/8/include/objc/Object.h
/usr/lib/gcc-cross/s390x-linux-gnu/8/include/objc/Protocol.h
/usr/lib/gcc-cross/s390x-linux-gnu/8/include/objc/message.h
/usr/lib/gcc-cross/s390x-linux-gnu/8/include/objc/objc-decls.h
/usr/lib/gcc-cross/s390x-linux-gnu/8/include/objc/objc-exception.h
/usr/lib/gcc-cross/s390x-linux-gnu/8/include/objc/objc-sync.h
/usr/lib/gcc-cross/s390x-linux-gnu/8/include/objc/objc.h
/usr/lib/gcc-cross/s390x-linux-gnu/8/include/objc/runtime.h
/usr/lib/gcc-cross/s390x-linux-gnu/8/include/objc/thr.h