How to repeat the problem on WinPython 3.4 64-bit on Windows 7 64-bit:

1. Install pycosat and conda using the binaries provided by Chris Gholke;
2. Do :
   conda init
   conda install mingw
3. What I did is I wrote a simple pyx code and tried to compile it using distutils described here: http://docs.cython.org/src/quickstart/build.html#building-a-cython-module-using-distutils
4. We can see that the conda-installed MinGW is not used.

A few points that stonebig and I discovered:

1. If I do where gcc, it will find conda-installed gcc.bat first. However, it is just not used.
2. If we prepend $WINPYDIR$\MinGW\bin at PATH in line 5 of the env.bat found in WinPythonDir\scripts, this problem goes away.