Define vcvars for msvc build, if they have not yet been. If vcvars not exist, show message that visual studio 2015 is not installed and where to download it.
Fixes#12948
Source-Repo: https://github.com/servo/servo
Source-Revision: 7aa0071e9b59db792742e1a47bd8577764a89fa7
This is the base PR for MSVC builds of servo and dependent crates. It's got replacements in the Cargo.toml to pull in the right versions, to make sure that crates were properly converted to CMake for all other platforms, not just Windows. (Servo builds with MSVC 2015 with this PR; also with 2013, though a manual change in rust-mozjs to select a different set of bindings is needed.)
This PR isn't quite ready yet, but I want bors-servo to do builds.
Source-Repo: https://github.com/servo/servo
Source-Revision: ec53136863f20b80caf165d2f15e8a77d614536e