penlight 1.4.0 changed how files are being globbed and busted hasn't
been updated accordingly yet.  See Olivine-Labs/busted#528 for more
information.

luarocks has had trouble in the past with multiple build/install
commands running at the same time.

Enable MSYS/MinGW builds in Appveyor

Add build recipe for libvterm in MinGW, a CMakeLists.txt
file is bundled in third-party/cmake/.

Added recipes to build bundled dependencies in native MinGW
toolchains - libuv, luajit, luarocks, msgpack

Using /MT was causing issues when building luarocks, revert it, use the
dynammic runtime and generate release DLLs for the dependencies.
Some refactoring was required because for linking cmake looks for the
import libraries (.lib) but on runtime executables we need the .dll files
to be in the same folder.

The DLLs are placed in the bin/ folder in order for nvim.exe to run
during the build and tests. The install target installs the DLLs with
the nvim binary - uses GetPrerequisites to find runtime DLLs.

Some minor issues that required adjustments:
- [MSVC] FindMsgpack.cmake now looks for msgpack_import.lib instead of
  msgpack.lib
- The lua-client fails to find libuv.lib, instead it looks for uv.lib,
  added second copy of the file to the install command.
- [MSVC] CMAKE_BUILD_TYPE affects the output paths, default to Release.

Part of these changes are credited to @jasonwilliams200OK who fixed the
third-party recipes to consistently use the same build type.

option: Do not expand options, obtained from XDG vars

Closes #5114.