ci: add configs for a CMake+Ninja build (#27)

Author: coryan

ci/kokoro/docker/build-in-docker-cmake.sh

@@ -58,6 +58,10 @@ if [[ "${CODE_COVERAGE:-}" == "yes" ]]; then
     "-DCMAKE_BUILD_TYPE=Coverage")
 fi
 
+if [[ "${USE_NINJA:-}" == "yes" ]]; then
+  cmake_flags+=( "-GNinja" )
+fi
+
 # Avoid unbound variable error with older bash
 if [[ "${#cmake_flags[@]}" == 0 ]]; then
   cmake "-H${SOURCE_DIR}" "-B${BINARY_DIR}"

ci/kokoro/docker/build.sh

@@ -78,6 +78,9 @@ elif [[ "${BUILD_NAME}" = "clang-3.8" ]]; then
   export DISTRO_VERSION=16.04
   export CC=clang
   export CXX=clang++
+elif [[ "${BUILD_NAME}" = "ninja" ]]; then
+  # Compiling with Ninja can catch bugs that may not be caught using Make.
+  export USE_NINJA=yes
 else
   echo "Unknown BUILD_NAME (${BUILD_NAME}). Fix the Kokoro .cfg file."
   exit 1
@@ -211,6 +214,10 @@ docker_flags=(
     # CMake builds use this flag.
     "--env" "CODE_COVERAGE=${CODE_COVERAGE:-}"
 
+    # If set to 'yes', use Ninja as the CMake generator. Ninja is more strict
+    # that Make and can detect errors in your CMake files, it is also faster.
+    "--env" "USE_NINJA=${USE_NINJA:-}"
+
     # If set, pass -DGOOGLE_CLOUD_CPP_CXX_STANDARD=<value> to CMake.
     "--env" "GOOGLE_CLOUD_CPP_CXX_STANDARD=${GOOGLE_CLOUD_CPP_CXX_STANDARD:-}"