Maybe aarch64-linux-gnu-gcc is not installed. Try

sudo apt-get install gcc-aarch64-linux-gnu

cc1plus is the internal front end program name for the Gnu Compiler Collection's C++ compiler. It's being called in this case because gcc has detected that test.cpp is a C++ file rather than a C file.

You would get it by installing the corresponding g++ package for the C compiler that you are using. For the aarch64-linux-gnu-gcc cross compiler, that would be g++-aarch64-linux-gnu I think.

You should then use aarch64-linux-gnu-g++ to compile your .cpp sources.

I’m guessing the problem is that your ARM toolchain is installed somewhere that’s not on root’s PATH; since you’re building with sudo, the compiler can’t be found.

To fix that, restore the correct ownership on all the files in the build tree:

sudo chown -R $USER .

(sudo is required here since you don’t own all the files.)

Now run the build without sudo:

make ARCH=arm CROSS_COMPILE=arm-linux-

The only part of the kernel build where you need to run it as root is the installation phases; since you’re cross-compiling you won’t ever need to do that on the build system (you’ll presumably be copying the built kernel and modules to another device, and installing them there).