Neither MinGW nor Cigwin are supported yet. But the build system has modular and quite clear design. So, you are welcome to contributeyour modules necessary for support of those compilers.
For MinGW, you canclone linux.gcc.inc file into windows.gcc.inc with fixingfor some windows-specifics (see windows.cl.inc).
AsI wrote insimilar topic, Cygwin looks rather like a separate platform than just a toolset for Windows. It requires implementation ofbuild/cygwin.inc and build/cygwin.gcc.inc files because settings of build/windows.inc don't fit into Cygwin's rules. And some modifications of common.inc are necessary to recognize Cygwin as a platform different from Windows.