Fix missing file libtaichi_c_api.so in Android App (#130)

scripts/build-android.sh

@@ -4,7 +4,10 @@ set -e
 rm -rf build-android-aarch64
 mkdir build-android-aarch64
 pushd build-android-aarch64
-TAICHI_C_API_INSTALL_DIR="${PWD}/../build-taichi-android-aarch64/install/c_api" cmake .. \
+
+C_API_DIR="${PWD}/../build-taichi-android-aarch64/install/c_api"
+
+TAICHI_C_API_INSTALL_DIR=${C_API_DIR} cmake .. \
     -DCMAKE_TOOLCHAIN_FILE="$ANDROID_NDK_ROOT/build/cmake/android.toolchain.cmake" \
     -DANDROID_PLATFORM=android-29 \
     -DANDROID_ABI="arm64-v8a" \
@@ -21,3 +24,19 @@ if [ $? -ne 0 ]; then
     exit -1
 fi
 popd
+
+# Check for libtaichi_c_api.so
+target_file="${PWD}/framework/android/app/src/main/jniLibs/arm64-v8a/libtaichi_c_api.so"
+source_file="${C_API_DIR}/lib/libtaichi_c_api.so"
+
+if [ ! -f "$target_file" ]; then
+    echo "File not found: $target_file"
+    echo "Copying from $source_file to $target_file"
+
+    cp "$source_file" "$target_file"
+    chmod 775 "$target_file"
+
+    echo "File copied and permissions set."
+else
+    echo "File already exists: $target_file"
+fi