* Add kokoro build for python source package

* Use libc++ for xcode 10 (#5303)

The xcode 10 removes the deprecated libstdc++ library. We could set
"MACOSX_DEPLOYMENT_TARGET" to "10.9" to use libc++ instead.

* Add python 3.7 build

* Add build for python 3.7 on linux and windows

* Remove unused source build

* Add comment

* Fix $MACOSX_DEPLOYMENT_TARGET mismatch

* Fix MACOSX_DEPLOYMENT_TARGET mismatch

* Add missing import for sysconfig

* Add missing imports

* Add kokoro config for building python wheels on windows

* Move script to root

* Debug

* Debug

* Change working directory

* Add msbuild to path

* Debug

* Fix python dir name

* Debug

* Move artifacts to targeted directory

* Update artifact directory

* Debug

* Debug

* Automatic generation of version

* Reduce file numbers

* Add config for building python wheel on mac

* Specify os name

* Clean up venv

* Debug

* Recover old path

* Add config for building python wheel

* Update submodules

* Fix setup.py to use c++11

* Fix syntax error

* Fix syntax error

* Add dir for artifact

* Update artifact dirctory

* Remove python 3.3

* Clean up virtual env

* Clean up env

* Test environment

* Test env variable

* Automatic update version number

* Remove dependency on python-wheel branch