Cherry-picked fix from #5406

* 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

Cherry-pick fix for compatibility with Python 3.7

Compilation of Python wrappers fails with Python 3.7 because
the Python folks changed their C API such that
PyUnicode_AsUTF8AndSize() now returns a const char* rather
than a char*. Add a patch to work around. Relates #4086.

Cherry-picked fix from PR #4650 into 3.6.x branch

* use flag_values = {"@bazel_tools//tools/cpp:compiler": "x"} for compiler config_settings

* Create compiler_config_setting.bzl

Include version information in Windows binaries (backport #4579 for 3.6.x)

Backport #4854 to 3.6.x

This should fix https://github.com/google/protobuf/issues/4717

This fixes issue #2610.

This was originally fixed in a101fa52 , but got
reverted by d36c0c53

Implements #3380

* 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

Backport building C# nuget to 3.6.x branch

This reverts commit c02346c72aafd1826b0397dbbce4ce04bf252f50.

* Check the message to be encoded is the wrong type. (#4885)

* Change TypeError to ArgumentError

This change only makes assertEquals pass for message in c extension. However, it actually does nothing.
This is the same behavior before 3.6.0 release.

Cherry-pick master build fixes and kokoro changes to 3.6.x

* Add continuous test for ruby 2.3, 2.4 and 2.5

* Change ruby 2.5 to 2.5.0

* No need to provide argument to rb_funcall when argc is 0

* Fix tests for ruby 2.5

* Use rescue instead of assert_raise to accept subclass of error

This avoids the need to use "yum update && yum upgrade" in the container
to be able to contact GitHub, which requires TLS 1.2[1].

I have verified that binaries built with this container still run in the
previous container; no errors like "/lib64/libc.so.6: version
`GLIBC_2.14' not found", which occur if using too new of a glibc when
compiling. CentOS 6.6 has glibc version 2.12 release 1.209.el6. CentOS
6.9 has glibc version 2.12 release 1.149.el6. Both would upgrade to
release 1.212.el6 via "yum update && yum upgrade".

1. https://githubengineering.com/crypto-deprecation-notice/

Now that we depend on C++11, we need at least GCC 4.8 instead of 4.7.
This change updates the Docker setup to continue using CentOS 6.6 but
with GCC 4.8.

I also added libm to the whitelist for dynamically linked libraries for
the ARM64 protoc binary.

* Remove js_embed binary.

1. Added C++ tests under the release docker image.
2. Cleaned up tests.sh and removed traivis stuff.