Warn or err on Windows if compiled with the "wrong" target_env

[filmor]

The Windows binaries distributed on erlang.org are compiled with MSVC, which leads to problems if a "gnu" (so "MinGW") environment is used, which is the default if people install Rust without having a Microsoft compiler toolchain installed.

It might make sense to ask the user for explicit confirmation (via a "force" environment variable?) at build time if a "windows-gnu" toolchain is used.