Auto merge of #4117 - brson:vs2017, r=alexcrichton
Auto merge of #4117 - brson:vs2017, r=alexcrichton

Update gcc crate for MSVC 2017

This is just a slightly more correct version of the gcc crate, but shouldn't have any practical changes.

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