add multi-platform build system
under `tools/` add some scripts to invoke the build system to build all deps for vbam and vbam itself: - `tools/linux/builder` This builds a mostly static linux binary with a few dynamic deps for xorg and wayland. Using gtk3. This will run on just about any dist. - `tools/osx/builder` Builds a static mac app targetting 10.7. - `tools/win/linux-cross-builder` Builds a static windows binary using the mingw-w64 toolchain. - `tools/win/msys2-builder` Builds a static windows binary in the MSYS2 environment, this may be suffering from a few regressions. Change some cmake code to support the build system, refactor a few things in it.