Use bazel 5 for bazel builds. (#4738)

* Use bazel 5 for Linux bazel builds.
* Download bazel 5.0.0 for macos and windows bazel builds.
* Modify the readme to mention bazel 5.0.0 as the version to use.

README.md

@@ -417,7 +417,7 @@ targets, you need to install CMake Version 2.8.12 or later.
 - [Python 3](http://www.python.org/): for utility scripts and running the test
 suite.
 - [Bazel](https://bazel.build/) (optional): if building the source with Bazel,
-you need to install Bazel Version 0.29.1 on your machine. Other versions may
+you need to install Bazel Version 5.0.0 on your machine. Other versions may
 also work, but are not verified.
 - [Emscripten SDK](https://emscripten.org) (optional): if building the
   WebAssembly module.

kokoro/macos-clang-release-bazel/build.sh

@@ -31,14 +31,14 @@ cd external && cd googletest && git reset --hard 1fb1bb23bb8418dc73a5a9a82bbed31
 git clone --depth=1 https://github.com/google/effcee              external/effcee
 git clone --depth=1 https://github.com/google/re2                 external/re2
 
-# Get bazel 0.29.1.
-gsutil cp gs://bazel/0.29.1/release/bazel-0.29.1-darwin-x86_64 .
-chmod +x bazel-0.29.1-darwin-x86_64
+# Get bazel 5.0.0
+gsutil cp gs://bazel/5.0.0/release/bazel-5.0.0-darwin-x86_64 .
+chmod +x bazel-5.0.0-darwin-x86_64
 
 echo $(date): Build everything...
-./bazel-0.29.1-darwin-x86_64 build :all
+./bazel-5.0.0-darwin-x86_64 build :all
 echo $(date): Build completed.
 
 echo $(date): Starting bazel test...
-./bazel-0.29.1-darwin-x86_64 test :all
+./bazel-5.0.0-darwin-x86_64 test :all
 echo $(date): Bazel test completed.

kokoro/scripts/linux/build-docker.sh

@@ -195,7 +195,7 @@ elif [ $TOOL = "android-ndk-build" ]; then
 
   echo $(date): ndk-build completed.
 elif [ $TOOL = "bazel" ]; then
-  using bazel-3.1.0
+  using bazel-5.0.0
 
   echo $(date): Build everything...
   bazel build :all

kokoro/windows-msvc-2015-release-bazel/build.bat

@@ -30,8 +30,8 @@ git clone --depth=1 https://github.com/google/effcee              external/effce
 git clone --depth=1 https://github.com/google/re2                 external/re2
 
 :: REM Install Bazel.
-wget -q https://github.com/bazelbuild/bazel/releases/download/0.29.1/bazel-0.29.1-windows-x86_64.zip
-unzip -q bazel-0.29.1-windows-x86_64.zip
+wget -q https://github.com/bazelbuild/bazel/releases/download/5.0.0/bazel-5.0.0-windows-x86_64.zip
+unzip -q bazel-5.0.0-windows-x86_64.zip
 
 :: Set up MSVC
 call "C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\vcvarsall.bat" x64