/usr/lib/gcc-cross/aarch64-linux-gnu/5/include/ is in libgcc-5-dev-arm64-cross 5.4.0-6ubuntu1~16.04.9cross1.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/gcc-cross/aarch64-linux-gnu/5/include-fixed/README
/usr/lib/gcc-cross/aarch64-linux-gnu/5/include-fixed/limits.h
/usr/lib/gcc-cross/aarch64-linux-gnu/5/include-fixed/linux/
/usr/lib/gcc-cross/aarch64-linux-gnu/5/include-fixed/linux/a.out.h
/usr/lib/gcc-cross/aarch64-linux-gnu/5/include-fixed/syslimits.h
/usr/lib/gcc-cross/aarch64-linux-gnu/5/include/arm_acle.h
/usr/lib/gcc-cross/aarch64-linux-gnu/5/include/arm_neon.h
/usr/lib/gcc-cross/aarch64-linux-gnu/5/include/backtrace-supported.h
/usr/lib/gcc-cross/aarch64-linux-gnu/5/include/backtrace.h
/usr/lib/gcc-cross/aarch64-linux-gnu/5/include/float.h
/usr/lib/gcc-cross/aarch64-linux-gnu/5/include/iso646.h
/usr/lib/gcc-cross/aarch64-linux-gnu/5/include/omp.h
/usr/lib/gcc-cross/aarch64-linux-gnu/5/include/openacc.h
/usr/lib/gcc-cross/aarch64-linux-gnu/5/include/sanitizer/
/usr/lib/gcc-cross/aarch64-linux-gnu/5/include/sanitizer/asan_interface.h
/usr/lib/gcc-cross/aarch64-linux-gnu/5/include/sanitizer/common_interface_defs.h
/usr/lib/gcc-cross/aarch64-linux-gnu/5/include/sanitizer/lsan_interface.h
/usr/lib/gcc-cross/aarch64-linux-gnu/5/include/stdalign.h
/usr/lib/gcc-cross/aarch64-linux-gnu/5/include/stdarg.h
/usr/lib/gcc-cross/aarch64-linux-gnu/5/include/stdatomic.h
/usr/lib/gcc-cross/aarch64-linux-gnu/5/include/stdbool.h
/usr/lib/gcc-cross/aarch64-linux-gnu/5/include/stddef.h
/usr/lib/gcc-cross/aarch64-linux-gnu/5/include/stdfix.h
/usr/lib/gcc-cross/aarch64-linux-gnu/5/include/stdint-gcc.h
/usr/lib/gcc-cross/aarch64-linux-gnu/5/include/stdint.h
/usr/lib/gcc-cross/aarch64-linux-gnu/5/include/stdnoreturn.h
/usr/lib/gcc-cross/aarch64-linux-gnu/5/include/unwind.h
/usr/lib/gcc-cross/aarch64-linux-gnu/5/include/varargs.h