modified meta.yaml to build for Windows with msys2

[tjwilli58]

Checklist

• [ ] Used a fork of the feedstock to propose changes
• [ ] Bumped the build number (if the version is unchanged)
• [ ] Reset the build number to 0 (if the version changed)
• [ ] Re-rendered with the latest conda-smithy
• [ ] Ensured the license file is being packaged.

[conda-forge-linter]

Hi! This is the friendly automated conda-forge-linting service.

I just wanted to let you know that I linted all conda-recipes in your PR (recipe) and found it was in an excellent condition.

[tjwilli58]

test:
  commands:
    - gst-inspect-1.0 --version
    - gst-launch-1.0  --version
    - gst-stats-1.0 --version       # [not win]
    - gst-typefind-1.0 --version

gst-stats-1.0 test fails if I don't filter it out

(condaforge) C:\Users\Tim\Miniconda3\envs\condaforge\conda-bld\gstreamer_1534031877041\test_tmp>call "C:\Users\Tim\Miniconda3\envs\condaforge\Scripts\activate.bat" "C:\Users\Tim\Miniconda3\envs\condaforge\conda-bld\gstreamer_1534031877041\_test_env"

(C:\Users\Tim\Miniconda3\envs\condaforge\conda-bld\gstreamer_1534031877041\_test_env) C:\Users\Tim\Miniconda3\envs\condaforge\conda-bld\gstreamer_1534031877041\test_tmp>IF 0 NEQ 0 exit 1

(C:\Users\Tim\Miniconda3\envs\condaforge\conda-bld\gstreamer_1534031877041\_test_env) ```
C:\Users\Tim\Miniconda3\envs\condaforge\conda-bld\gstreamer_1534031877041\test_tmp>call "C:\Users\Tim\Miniconda3\envs\condaforge\conda-bld\gstreamer_1534031877041\test_tmp\run_test.bat"

(C:\Users\Tim\Miniconda3\envs\condaforge\conda-bld\gstreamer_1534031877041\_test_env) C:\Users\Tim\Miniconda3\envs\condaforge\conda-bld\gstreamer_1534031877041\test_tmp>gst-inspect-1.0 --version
WARNING: no real random source present!
gst-inspect-1.0 version 1.14.2
GStreamer 1.14.2
Unknown package origin

(C:\Users\Tim\Miniconda3\envs\condaforge\conda-bld\gstreamer_1534031877041\_test_env) C:\Users\Tim\Miniconda3\envs\condaforge\conda-bld\gstreamer_1534031877041\test_tmp>IF 0 NEQ 0 exit /B 1

(C:\Users\Tim\Miniconda3\envs\condaforge\conda-bld\gstreamer_1534031877041\_test_env) C:\Users\Tim\Miniconda3\envs\condaforge\conda-bld\gstreamer_1534031877041\test_tmp>gst-launch-1.0  --version
gst-launch-1.0 version 1.14.2
GStreamer 1.14.2
Unknown package origin

(C:\Users\Tim\Miniconda3\envs\condaforge\conda-bld\gstreamer_1534031877041\_test_env) C:\Users\Tim\Miniconda3\envs\condaforge\conda-bld\gstreamer_1534031877041\test_tmp>IF 0 NEQ 0 exit /B 1

(C:\Users\Tim\Miniconda3\envs\condaforge\conda-bld\gstreamer_1534031877041\_test_env) C:\Users\Tim\Miniconda3\envs\condaforge\conda-bld\gstreamer_1534031877041\test_tmp>gst-stats-1.0 --version
'gst-stats-1.0' is not recognized as an internal or external command,
operable program or batch file.

(C:\Users\Tim\Miniconda3\envs\condaforge\conda-bld\gstreamer_1534031877041\_test_env) C:\Users\Tim\Miniconda3\envs\condaforge\conda-bld\gstreamer_1534031877041\test_tmp>IF 9009 NEQ 0 exit /B 1

(C:\Users\Tim\Miniconda3\envs\condaforge\conda-bld\gstreamer_1534031877041\_test_env) C:\Users\Tim\Miniconda3\envs\condaforge\conda-bld\gstreamer_1534031877041\test_tmp>IF 1 NEQ 0 exit 1
Tests failed for gstreamer-1.12.5-hfa6e2cd_1.tar.bz2 - moving package to C:\Users\Tim\Miniconda3\envs\condaforge\conda-bld\broken
WARNING:conda_build.build:Tests failed for gstreamer-1.12.5-hfa6e2cd_1.tar.bz2 - moving package to C:\Users\Tim\Miniconda3\envs\condaforge\conda-bld\broken
removing: gstreamer-1.12.5-hfa6e2cd_1.tar.bz2
TESTS FAILED: gstreamer-1.12.5-hfa6e2cd_1.tar.bz2