Use option to identify standalone

lsplant/build.gradle.kts

@@ -114,6 +114,7 @@ android {
                     cFlags += flags
                     arguments += "-DANDROID_STL=none"
                     arguments += "-DCMAKE_BUILD_TYPE=Release"
+                    arguments += "-DLSPLANT_STANDALONE=ON"
                 }
             }
         }

lsplant/src/main/jni/CMakeLists.txt

@@ -8,7 +8,7 @@ if (CCACHE)
     set(CMAKE_C_COMPILER_LAUNCHER ${CCACHE})
 endif ()
 
-if ("${ANDROID_STL}" STREQUAL "none")
+if (LSPLANT_STANDALONE)
     find_package(cxx REQUIRED CONFIG)
     link_libraries(cxx::cxx)
 endif()