Switch to Ninja for building the native runtime

The version of `make` provided in the MSYS2 does not work well with CMake on
Windows. This makes it impossible to do incremental nativeruntme builds on
Windows.

See https://stackoverflow.com/questions/2401976 for more details on the issue.

Switch to using Ninja everywhere, which seems to be more reliable across
platforms.

PiperOrigin-RevId: 413717789

.github/workflows/build_native_runtime.yml

@@ -32,6 +32,14 @@ jobs:
         with:
           java-version: 11.0.8
 
+      - name: Install Ninja (Mac OS)
+        if: runner.os =='macOS'
+        run: brew install ninja
+
+      - name: Install Ninja (Linux)
+        if: runner.os =='Linux'
+        run: sudo apt-get install ninja-build
+
       - name: Cache ICU build output
         id: cache-icu
         uses: actions/cache@v2
@@ -61,8 +69,8 @@ jobs:
         run: |
           mkdir build
           cd build
-          ICU_ROOT_DIR=$HOME/icu-bin cmake -B . -S ../nativeruntime/cpp
-          make
+          ICU_ROOT_DIR=$HOME/icu-bin cmake -B . -S ../nativeruntime/cpp -G Ninja
+          ninja
 
       - name: Rename libnativeruntime for Linux
         if: runner.os == 'Linux'

.github/workflows/tests.yml

@@ -52,6 +52,10 @@ jobs:
           make -j4
           make install
 
+      - name: Install Ninja (Linux)
+        if: runner.os =='Linux'
+        run: sudo apt-get install ninja-build
+
       - name: Build
         run: ICU_ROOT_DIR=$HOME/icu-bin SKIP_ERRORPRONE=true SKIP_JAVADOC=true ./gradlew clean assemble testClasses --parallel --stacktrace --no-watch-fs
 
@@ -93,6 +97,10 @@ jobs:
           path: ~/icu-bin
           key: ${{ runner.os }}-${{env.CPU_ARCH}}-icu-${{ hashFiles('nativeruntime/external/icu/**') }}
 
+      - name: Install Ninja
+        if: runner.os =='Linux'
+        run: sudo apt-get install ninja-build
+
       - name: Run unit tests
         run: |
           ICU_ROOT_DIR=$HOME/icu-bin SKIP_ERRORPRONE=true SKIP_JAVADOC=true ./gradlew test --info --stacktrace --continue \

nativeruntime/build.gradle

@@ -29,7 +29,7 @@ task cmakeNativeRuntime {
     mkdir "$buildDir/cpp"
     exec {
       workingDir "$buildDir/cpp"
-      commandLine 'cmake', "-B", ".", "-S","$projectDir/cpp/"
+      commandLine 'cmake', "-B", ".", "-S","$projectDir/cpp/", "-G", "Ninja"
     }
   }
 }
@@ -80,7 +80,7 @@ task makeNativeRuntime {
   doLast {
     exec {
       workingDir "$buildDir/cpp"
-      commandLine 'make'
+      commandLine 'ninja'
     }
   }
 }