* cleanup C# win artifact build
* build C# basictests on win with ninja
* specify default parallelism for C# win artifact
* honor GRPC_PYTHON_BUILD_EXT_COMPILER_JOBS in build_artifact_python.bat
* set --inner_jobs for windows grpc_build_artifact job
* fixup C# build picking env variables from C core build
* get rid of no longer needed NativeDependenciesConfiguration C# setting
* Download the working msys64 and use it to compile 27
* Remove the cygwin detection override logic
* Only install Python interpreters in jobs running on winserver2016
* Fix the batch script substring check
* Increase the timeout for related jobs
* TIL that there is an allow list for Kokoro env vars
* Download the working msys64 and use it to compile 27
* Remove the cygwin detection override logic
* Only install Python interpreters in jobs running on winserver2016
* Fix the batch script substring check
* Increase the timeout for related jobs
* TIL that there is an allow list for Kokoro env vars
Removes MinGW flags from various build scripts, since they're now set in
our `setup.py`s by default. Also removes the arguments for the
extensions in grpcio's setup.py; that function was already accessing
globals anyway, might as well go whole-hog.
The default compiler for Python c extensions is VS2008
or VS2010 depending on the Python version. Since c-core
moved onto the c99 standard, these compilers are not
compatible.