[CMake] Remove supporting of DEFAULT_SYSROOT for the ARM/Aarch64 cross builds. NFC. (#94300)

Avoid usage DEFAULT_SYSROOT CMake variable to confgiure the ARM/Aarch64
cross platform toolchain builds. Use the Clang configuration files with
proper `--sysroot=` in it instead.

More details could be found here:
    https://github.com/llvm/llvm-project/issues/94284