I haven't tested linking and execution yet; it would probably require to
use e.g. `mingw-w64-ucrt-x86_64-go` from MSYS2 (instead of
`mingw-w64-x86_64-go` where the stdlib clashes).
* Use CMake's command mode to set environment variables
* Only make use of `CMAKE_RANLIB` if set
* Avoid using the compiler/tools/flags from CMake via cgo when building
with MSVC as this doesn't work; this is problematic because stdlibs will
not necassarily match but this way we can at least compile the static
library
* Do *not* build Syncthing in addition as standalone executalbe
* Explose instead all of Syncthing's commands via the library
interface
* Make all of Syncthing's commands (including `serve`) accessible
via Syncthing Tray's executable
* Remove copied code for directory creation and instead use
upstream's code directly