for checking libs for WANTLIB, use objdump -p or readelf -d and look at NEEDED ldd also shows you libraries pulled in by dep's
> I haven't verified this is the reason, but a quick grep in Rust source
> tree found this in library/unwind/build.rs:
>
> } else if target.contains("openbsd") {
> if target.contains("sparc64") {
> println!("cargo:rustc-link-lib=gcc");
> } else {
> println!("cargo:rustc-link-lib=c++abi");
> }
> } else if target.contains("solaris") {
>
so I guess kn's test was on sparc64
