Auto merge of #3775 - alexcrichton:version-info, r=alexcrichton
Auto merge of #3775 - alexcrichton:version-info, r=alexcrichton

Prefer CARGO_PKG_* in version info

These are always set by Cargo and avoids rustbuild-building-cargo to need to
parse semver

rustyhorde/cargo,tshepang/cargo,durka/cargo,nipunn1313/cargo,durka/cargo,rust-lang/cargo,durka/cargo,achanda/cargo,vojtechkral/cargo,eminence/cargo,achanda/cargo,vojtechkral/cargo,tsurai/cargo,nipunn1313/cargo,vojtechkral/cargo,rust-lang/cargo,tshepang/cargo,nipunn1313/cargo,eminence/cargo,rust-lang/cargo,nipunn1313/cargo,tsurai/cargo,eminence/cargo,rustyhorde/cargo,tsurai/cargo,eminence/cargo,tsurai/cargo,achanda/cargo,achanda/cargo,rustyhorde/cargo,durka/cargo,tshepang/cargo,tsurai/cargo,rust-lang/cargo,vojtechkral/cargo,tshepang/cargo,rustyhorde/cargo