* Down-integrate internal changes to github.

* fix python conformance test

* fix csharp conformance test

* add back java map_lite_test.proto's optimize for option

* fix php conformance test

* Down-integrate internal changes

* Update generated code for php, objc and csharp.

* Add missing dependency in conformance_php

* Update README.md

This reverts commit 93f6b67e.

Protoc adds already the relative path to the output directory.
Therefore, we have to remove this again from the output directory
to prevent adding it twice.

I want to use the conformance tests from upb, which is switching
to CMake.

Implements #3380

* Fixes https://github.com/google/protobuf/issues/5031
* Fixes https://github.com/google/protobuf/issues/5037

* Delete unused files.

* Remove js_embed binary.

Without this fix, protobuf_generate() sets the variable _generated_srcs to
${protobuf_generate_PROTOC_OUT_DIR}/${_rel_dir}/${_basename}${_ext}
but generates the files in
${protobuf_generate_PROTOC_OUT_DIR}/${_basename}${_ext}

* Remove js_embed binary.

* CMake: Add comment for CMP0048

* CMake: osx use @rpath/ as target's install name (CMP0042)

On MacoS library should use @rpath/ as prefix path instead of absolute build path
e.g. otool -L libprotobuf.dylib
libprotobuf.dylib:
  @rpath/libprotobuf.dylib (...)
  ...

* CMake: add rpath to target for LINUX and APPLE

- merge loop for .h and .proto includes
- fix shellcheck errors

For google/or-tools, on windows, we need to use `import "google/protobuf/wrappers.proto";` since we want "optional" int64 and in version3 POD get default value...
-> so we use "google.protobuf.Int64Value" since 0 is a valid value and different from "not set" for our use case.

CMakeLists.txt adds c++11 flags for clang

Add googletest as a submodule in third_party/googletest.

This reverts commit 724f0be3.