Explicitly setting `CMAKE_Fortran_COMPILER=gfortran` on Windows.
Explicitly setting `CMAKE_Fortran_COMPILER=gfortran` on Windows.

A build [1] has failed with

```
CMake Error at C:/Miniconda/conda-bld/libbezier_1580880865251/_build_env/Library/share/cmake-3.16/Modules/CMakeTestFortranCompiler.cmake:45 (message):
  The Fortran compiler

    "C:/Miniconda/conda-bld/libbezier_1580880865251/_build_env/Library/bin/flang.exe"

  is not able to compile a simple test program.

  It fails with the following output:

    Change Dir: C:/Miniconda/conda-bld/libbezier_1580880865251/work/build/CMakeFiles/CMakeTmp

...

-- The Fortran compiler identification is Flang 99.99.1
-- The C compiler identification is GNU 8.1.0
-- Check for working Fortran compiler: C:/Miniconda/conda-bld/libbezier_1580880865251/_build_env/Library/bin/flang.exe
-- Check for working Fortran compiler: C:/Miniconda/conda-bld/libbezier_1580880865251/_build_env/Library/bin/flang.exe  -- broken
-- Configuring incomplete, errors occurred!
```

[1]: https://dev.azure.com/conda-forge/feedstock-builds/_build/results?buildId=117712&view=logs&j=240f1fee-52bc-5498-a14a-8361bde76ba0&t=78a0099b-3f13-5ae9-c1f0-24f71d1eac20

Juanlu001/staged-recipes,igortg/staged-recipes,jakirkham/staged-recipes,ReimarBauer/staged-recipes,mariusvniekerk/staged-recipes,chrisburr/staged-recipes,mariusvniekerk/staged-recipes,stuertz/staged-recipes,conda-forge/staged-recipes,patricksnape/staged-recipes,jochym/staged-recipes,kwilcox/staged-recipes,petrushy/staged-recipes,dschreij/staged-recipes,scopatz/staged-recipes,asmeurer/staged-recipes,johanneskoester/staged-recipes,jochym/staged-recipes,igortg/staged-recipes,kwilcox/staged-recipes,Juanlu001/staged-recipes,petrushy/staged-recipes,dschreij/staged-recipes,ReimarBauer/staged-recipes,patricksnape/staged-recipes,SylvainCorlay/staged-recipes,ocefpaf/staged-recipes,goanpeca/staged-recipes,johanneskoester/staged-recipes,jakirkham/staged-recipes,hadim/staged-recipes,scopatz/staged-recipes,SylvainCorlay/staged-recipes,hadim/staged-recipes,conda-forge/staged-recipes,stuertz/staged-recipes,birdsarah/staged-recipes,chrisburr/staged-recipes,birdsarah/staged-recipes,asmeurer/staged-recipes,goanpeca/staged-recipes,ocefpaf/staged-recipes