Update gtest to 1.11.0 (#1086)

Properly resolves #1083, #996.

test/gtest-1.11.0/docs/platforms.md

@@ -0,0 +1,35 @@
+# Supported Platforms
+
+GoogleTest requires a codebase and compiler compliant with the C++11 standard or
+newer.
+
+The GoogleTest code is officially supported on the following platforms.
+Operating systems or tools not listed below are community-supported. For
+community-supported platforms, patches that do not complicate the code may be
+considered.
+
+If you notice any problems on your platform, please file an issue on the
+[GoogleTest GitHub Issue Tracker](https://github.com/google/googletest/issues).
+Pull requests containing fixes are welcome!
+
+### Operating systems
+
+*   Linux
+*   macOS
+*   Windows
+
+### Compilers
+
+*   gcc 5.0+
+*   clang 5.0+
+*   MSVC 2015+
+
+**macOS users:** Xcode 9.3+ provides clang 5.0+.
+
+### Build systems
+
+*   [Bazel](https://bazel.build/)
+*   [CMake](https://cmake.org/)
+
+Bazel is the build system used by the team internally and in tests. CMake is
+supported on a best-effort basis and by the community.