The build was previously failing with `error: unknown command: -print-file-name=libstdc++.a`
because the command invocation was
`zig -print-file-name=libstdc++.a`
instead of
`zig c++ -print-file-name=libstdc++.a`

note: .cxx_compiler_arg1 = "" instead of undefined to avoid breaking existing setups without requiring to run cmake again.