Download and install mingw and msys (base configuration for each). I used msys 1.0 and mingw "TDM-GCC 4.7.1 32-bit".
Add to windows path. Run the following commands in the cflow distribution directory-
bash configure
make
After building, executable is available under src. Prebuilt executable stored in project root.
Install msys-2 for x86_64 (these instructions are helpful: http://stackoverflow.com/a/30071634). Then run as above (correcting path etc to run correct tools).
I installed msys2: https://www.msys2.org/
Then installed some packages:
pacman -S --needed \
base-devel \
mingw-w64-i686-toolchain \
mingw-w64-x86_64-toolchain \
msys2-devel
To run the build:
# include mingw in PATH
export PATH=$PATH:/c/msys64/mingw32/bin
./configure
make -j 6
cflow sources are GPL v3. everything else is public domain.