lang/rust and www/curl with http2 option

[Adam <adam%netbsd.org@localhost>]

Greetings,

While trying to fix lang/rust on Darwin, I came across a linking problem which occurs with its internal curl library. (Described here https://github.com/alexcrichton/curl-rust/issues/279, but their solution does not work for me.) It is build by curl-sys module, which checks if curl with http2 support exists in the system. Apple provides such a library with macOS, but it is usually shadowed by curl from PkgSrc which does not have http2 option enabled by default. When I enable http2 for www/curl, when Rust builds and links correctly.

So, I propose enabling http2 as default for www/curl and "buildlinking" lang/rust with www/curl. That way we would provide more modern curl, and introduce a dependency on www/nghttp2, but Rust should build correctly.

Comments are welcome. :)

Kind regards,
Adam