Removed arena_nc.cc and arena_nc_test.py

This test is undocumented and it looks like it has probably never
worked. Let's just remove it to tidy things up. This fixes issue #2515.

Fix warning in compiler/js/embed.cc

embed.cc: In function ‘std::string CEscape(const string&)’:
embed.cc:51:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (int i = 0; i < str.size(); ++i) {
                                ^

Init index_in_metadata_ without condition

Eliminate redundant methods in C++ generated code for lite protos

Chromium MemorySanitizer (MSan) reports use-of-uninitialized-value
of index_in_metadata_ attribute from EnumGenerator class. Fix these
warnings by initializing these attributes without condition.

Added Bazel genrule for generating well_known_types_embed.cc

In pull request #2517 I made this change for the CMake and autotools
builds but forgot to do it for the Bazel build.

Add rvalue setters for non-arena strings on C++11.

Remove spurious NULL checks in ArenaStringPtr::CreateInstance.

Auto-generate well_known_types_embed.cc

The check target did not depend on the test_plugin binary, so this would
cause "make check" to fail at times because of the absence of
test_plugin. This change adds a dependency on test_plugin so that it
will always get built before the tests are executed.

Until now this file was just checked into the repo, but actually it
should be generated from any.js, struct.js, and timestamp.js. This
change updates the build system to make this happen. To make it work I
also had to remove some C++11 features from embed.cc.

Missed LIBPROTOC_EXPORT for GRPC added

Fixes #2511.

Define LANG_CXX11 for port.h and use this to guard C++11 features.

Removed Android-specific code from stubs/hash.h

Fixes and expands comments on how to use GPB_ENUM_FWD_DECLARE

This is basic and more tests will be added over time.

Fix integer overflow in FastUInt32ToBufferLeft

Add missing includes

Add support for Windows ARM builds

If digits > 2, and int is 32 bit, line 999 overflows. It has been fixed
internally in CL 41203823.

This #ifdef in hash.h causes us to give up on finding a hash function on
Android, when there do seem to be hash functions available in practice.
I also had to tweak a macro in map.h that was disabling on Android an
allocator construct() method that we need.

This changes fixes "error C2039: 'getline': is not a member of 'std'"
compilation error.

remove leading whitespace in C# xml comments

This changes fixes "use of undeclared identifier 'INT_MAX'"
compilation error.

Fix #include in cc files

Add a badge for bazel build status.