build.rs: FreeBSD support

[valpackett]

• emit_std_cpp_link: ("freebsd", _) is like ("macos", _), we use libc++
• in the big match (target_os.as_str(), target_env.as_str()), it would make sense to move ("linux", _) code to (_, _) so that it works on any unix-like platform, and use emit_std_cpp_link there instead of hardcoding stdc++
• a default search dir of "/usr/local/lib" for target_os == "freebsd" would be nice
• also a way to force using the shared lib when combined exists..

[valpackett]

Please at least do the libc++ thing, anything depending on unmodified shaderc-rs is literally unusable because the -lstdc++ linker argument makes everything blow up :(

[antiagainst]

Thanks for the comment. But I'm not familiar with FreeBSD and don't have a FreeBSD environment for developing to make sure everything functions properly. If you can send a pull request that would be awesome!

[valpackett]

Well, there's the whole CLA thing. I don't remember if the CLA form requires lots of personal information still, but I can't even sign into the google account for my current email address because it insists on a phone number >_<

Anyway my previous comment is a bit wrong, there's actually no -lstdc++, just lack of -lc++.

You can get away with no testing, I have already tested the following very obvious changes: just treat "freebsd" exactly as "macos" in these three places:

shaderc-rs/shaderc-sys/build/build.rs

Line 168 in 5784243

if target_os == "macos" {

shaderc-rs/shaderc-sys/build/build.rs

Line 277 in 5784243

("macos", _) => {

shaderc-rs/shaderc-sys/build/build.rs

Line 345 in 5784243

("macos", _) => println!("cargo:rustc-link-lib=dylib=c++"),