CMake: Linux->Linux(non-static), Windows(MinGW)->Windows

[trustytrojan]

• Adding another build system option, not replacing autotools
  • It is able to build on Linux for Linux, and on Windows with MinGW for Windows
  • The added CMake files are under a build-contrib folder as to not be confused with the cmake-win system for MSVC
• Helps for Windows to Windows builds when you don't want a VS installation on your system
• Due to CMake quirks I'm not gonna bother making an as-static-as-possible Linux build. How static it ends up depends on how many dependencies you have installed system-wide (same as --enable-system-deps with autotools)
• Configure command: cmake -Sbuild-contrib -Bbuild
• Build command: cmake --build build --parallel

[kiwec]

This changes files in cmake-win/ and src/, is that needed for it to work?

[trustytrojan]

The *_LINUX_URL variables in dependencies.cmake, yes, for Linux builds. The if(WIN32) in binclude.cmake, most likely, because I'm not sure what would happen if you tell the assembler to make a "win64" object on Linux. Regardless, this isn't affecting the MSVC build as WIN32 is always true on Windows.