Support propagating warnings from build.rs #103
Description
Right now running cargo build, cargo check or cargo clippy doesn't produce any warnings from build.rs.
It is possible to propagate them using cargo::warning=MESSAGE.
I think some kind of flag would be nice that converts corresponding warnings lines to lines prefixed with cargo::warning=.
Probably not in scope, but it'd also be nice to do something about compiling the whole thing when called under clippy, I'd prefer for it to just run clippy on the source code (I can work around the fact that no shader is produced by spirv builder in my build.rs.
Originally mentioned in #101 (comment)