Currently pkg-config-rs tries to prevent incorrect use of pkg-config for cross-compilation:

Cross compilation detected. Use PKG_CONFIG_ALLOW_CROSS=1 to override

However, judging by questions on the Rust forum, users don't understand the problem. They only set the variable as instructed, and are disappointed that it still doesn't work.

I suggest changing this message to point users to a more complete explanation, e.g:

pkg-config must be configured for cross-compilation. See https://github.com/rust-lang/pkg-config-rs#how-to-cross-compile

which would then instruct users to set sysroot, etc. first before enabling PKG_CONFIG_ALLOW_CROSS=1.