tests: Use specific version of gtest for CI

.appveyor.yml

@@ -30,6 +30,9 @@ before_build:
   - python scripts/update_deps.py --dir=external
   # Get Google Test
   - git clone https://github.com/google/googletest.git external/googletest
+  - cd external/googletest
+  - git checkout tags/release-1.8.1
+  - cd %APPVEYOR_BUILD_FOLDER%
   # Generate build files using CMake for the build step.
   - echo Generating CMake files for %PLATFORM%
   - mkdir build

.travis.yml

@@ -61,6 +61,9 @@ before_install:
       python scripts/update_deps.py --dir=external $UPDATE_DEPS_EXTRA_OPTIONS
       # Get Google Test
       git clone https://github.com/google/googletest.git external/googletest
+      pushd ${TRAVIS_BUILD_DIR}/external/googletest
+      git checkout tags/release-1.8.1
+      popd
     fi
   - |
     if [[ "$CHECK_FORMAT" == "ON" && "$TRAVIS_PULL_REQUEST" != "false" ]]; then

BUILD.md

@@ -81,6 +81,8 @@ To obtain the framework, change your current directory to the top of your
 Vulkan-Loader repository and run:
 
     git clone https://github.com/google/googletest.git external/googletest
+    cd external/googletest
+    git checkout tags/release-1.8.1
 
 before configuring your build with CMake.