Add build support for MINGW64 and partially fix static linking problem
Add build support for MINGW64 and partially fix static linking problem

libcurl.a provided by msys2 links with wrong nghttp, that leads static linking problem. The change to LDFLAGS still could not sucessfully linked with libcurl.a provided by msys2, but we can use libcurl.a provided [here](https://curl.haxx.se/windows/) instead.
selsta/hlsdl