Cygwin Ports support for OPAM depext

Primitive wrapper around cygcheck and cygwin's setup-x86.exe or setup-x86_64.exe.

• add /usr/i686-w64-mingw32/sys-root/mingw/bin or /usr/x86_64-w64-mingw32/sys-root/mingw/bin to your $PATH (in front of /bin, not after it!)

• opam install depext depext-cygwinports

$ opam depext zarith mikmatch_pcre sqlite3
$ opam install zarith mikmatch_pcre sqlite3

• Cygwin Ports
• opam-depext