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

1. Changed maven script to only do artifact uploading and removed build
script invocation from it. We didn't use maven to invoke the build
script before (we built protoc manually and editted pom.xml to only do
uploading for previous releases), and will not use it in the future (we
will use kokoro to build artifacts).
2. Cleaned up build-protoc.sh and README.md: removed the part about
using maven to build and listed supported platforms explicitly.

Add kokoro bazel configs to 3.6.x branch.

Additional support for building and deploying ppcle_64 artifacts

Fix initialization with Visual Studio

It appears that Visual Studio does not work well with std::once_flag
because it has a bug causing it to initialize that during dynamic
initialization instead of constant initialization. This change works
around the problem by using function static initializers instead.

@gerben-s originally wrote this change for the Google-internal codebase
but I am just cherry-picking it here.

This fixes #4773.

* Install rake compiler

* Add kokoro config to build ruby gem on linux

* Rename from linix to linux

* Fix prepare_build.sh name

* Clean up

* Install bundler

* Install bundler

* Use c99 in order to build gem on mingw-32 on ruby 2.0.0

See https://github.com/rake-compiler/rake-compiler-dock/issues/4

* Move c99 config to extcofig.rb

* Add files to build ruby artifact for mac on kokoro

* Move ruby specific stuff to ruby dir

This configuration builds both 32-bit and 64-bit binaries for Mac OS X.
One thing I had to change was to increase our minimum supported version
for 10.7 to 10.9, because 10.9 (Mavericks) appears to be the earliest
version supporting C++11.

* Work around MSVC issue with std::atomic initialization

MSVC seems to have a bug where it does not use constant initialization
for std::atomic, which ends up causing crashes during initialization.
This change introduces a workaround by putting the std::atomic inside a
union, which causes the compiler to use constant initialization for it.

* Added an AppVeyor test for static linking with MSVC

This should make it easy to automatically build 32-bit and 64-bit
Windows protoc binaries.

* Use legacy name in php runtime

Old generated code cannot work with new runtime, because the new runtime
assumes new class name for nested message. For details see #4738.

* Remove unused method

Updated the change log with changes for 3.6.0

Cherry-picked XCode 10 fixes into 3.6.x branch

* Update code to work for Xcode 10b

* Update README and test scripts to mention that Xcode 7 is no longer supported

Require C++11 and pass -std=c++11

This commit updates the Autotools build to require a C++11 compiler and
explicitly pass -std=c++11. This seems to be necessary for enabling
C++11 support in older compilers.

Cherry-pick changes into 3.6.x

These methods are used by grpc

Removed duplicate using statement from ReflectionUtil.cs

Fix php memory leak test (#4692)