Three new builds (GL, GLES2, GLES3), Vulkan is now built with just MSVC
2019; removed 2015 RT builds because nobody cares and axed also GLES
2015 builds. In total it's one build less (well, the RT ones are
really slow, so way more than that in fact). Yay!
Disabling everything that doesn't depend on Vulkan as it's not needed to
be built again -- that's basically everything right now. This needs to
be a separate build for the foreseeable future, because it requires a
newer CMake version for the Find module and it'll probably also require
newer C++ standard.
Thanks to @LB-- for providing me with an oneliner to compile a file with
cl.exe.