* Add support for building with MinGW

Tested with MSYS2 MinGW 8.3.0, gcc-mcf.lhmouse MinGW 9.2.1,
and StephanTLavavej/mingw-distro!

* Add MinGW toolchain

From your MinGW configured shell you could just use vcpkg to
configure packages.

An x64-mingw triplet would look like:
```
set(VCPKG_TARGET_ARCHITECTURE x64)
set(VCPKG_CRT_LINKAGE dynamic)
set(VCPKG_LIBRARY_LINKAGE static)
set(VCPKG_ENV_PASSTHROUGH PATH)

set(VCPKG_CMAKE_SYSTEM_NAME MinGW)
```

* Add MinGW community tripplets

x64 tested with https://github.com/StephanTLavavej/mingw-distro
x86, arm64, arm tested with https://github.com/mstorsjo/llvm-mingw

* Move untested triplets to Community Triplets

* Document community triplets

* Load community triplets by default and alert when using one

* [triplets] Merge documentation of community triplets

* Bump version

* Add preliminary support for arm-windows and arm64-windows triplets

Visual Studio 15.4 shipped with new VC tools targeting arm and arm64
for desktop. This change allows for recognition and usage of new
triplets supporting arm and arm64 Windows desktop and server targets.

* Remove unnecessary changes

* Part 2

* Part 3

* Make detection of Arm64 _VCPKG_TARGET_ARCHITECTURE precise

* Enforce usage of Visual Studio CMake generatorfor arm and temporarily arm64 targets

* Address code review feedback, clean libjpeg-turbo port.cmake

* [libjpeg-turbo][tiff] Reduce changes to existing libraries.

* [vcpkg-cmake] Simplify toolchain selection logic and improve comments

dynamic or static