Fix cpp benchmark dependency on mac

Merge 3.6.x into master

Fix initialization with Visual Studio

protoc-artifacts: Update centos base from 6.6 to 6.9

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/

Updated Docker setup to use GCC 4.8

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.

Fix SFINAE in 'RepeatedPtrFieldBase::Add'

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.

Without this the error of un-moveable GenericTypeHandler will pop until
'TypeHandler::New(arena_, std::move(value))' is called.

* Update message_module.cc

Add missing piece from pull request #4698:  actually initialize the new API object.

* Update message_module.cc

Fix bazel build of examples.

Add global extension registry to the repo.

* 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

Handle srcs in generated files by cd'ing in and out

Ruby JSON encoding omits zero-length repeated fields by default.

Feat: add import-style=commonjs_strict option to the compiler

Google::Protobuf::Struct can access a missing key (#3846)

Missing symbol exports for Windows DLL

Remove write-strings warning from COPTs

Add wsrpc

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

Fix to allow a compilation under mips big endian with gcc

Internal convert file was broken. Change the capsule to the correct name

This change reduces the excessive warnings when compiling C++ protobufs like "external/protobuf_archive/python/google/protobuf/pyext/message.cc:2629:1: warning: ISO C++ forbids converting a string constant to 'char*' [-Wwrite-strings]"

The __MIPSEL__ is mips little endian, specific and we needed
to compile for a big endian mips target that also happened
to be a mips64, so replaced the __MIPSEL__ with a __mip__
which should preserve the build on little endian and allow a
build for a big endian setup.

	$ echo | mips64-linux-gcc -E -dM -
	... snip snip ...
	#define __mips__ 1
	#define __MIPSEB__ 1
Signed-off-by: Charles Hardin <ckhardin@gmail.com>

* Add -Og to no-warning-test

* Initialize value

* Implement PrintFieldName in CompactRepeatedFieldPrinter to prevent Woverloaded-virtual

* Update generated code

* This allows for ruby code to catch and handle Protobuf
    TypeErrors separately from the standard Ruby TypeError

  * Maintains backwards compatibility by having the new
    Google::Protobuf::TypeError inherit from the base
    TypeError. Any code that was catching TypeError should
    continue to work.

Removed forward declaration of MemBlock class

Removed forward declaration of MemBlock class.

Declaration is in conflict with declaration `::strings::MemBlock`

Merge 3.6.x branch into master