Some of the example not compiled with Android

/opt/android/android-ndk-r18b/toolchains/llvm/prebuilt/linux-x86_64/bin/clang++
 -D__ANDROID_API__=21 -target aarch64-none-linux-android -gcc-toolchain 
/opt/android/android-ndk-r18b/toolchains/aarch64-linux-android-4.9/prebuilt/linux-x86_64
 -Wl,--exclude-libs,libgcc.a 
--sysroot=/opt/android/android-ndk-r18b/platforms/android-21/arch-arm64/
 -Wl,-soname,libcalculator.so 
-Wl,-rpath=/home/qt/RTA/qt5/5.12.1/android_arm64_v8a/lib 
-Wl,-rpath-link=/home/qt/RTA/qt5/5.12.1/android_arm64_v8a/lib 
-Wl,--no-undefined -Wl,-z,noexecstack -shared -o libcalculator.so main.o
 qrc_calculator.o   -L/home/qt/RTA/qt5/5.12.1/android_arm64_v8a/lib 
-lQt5UiTools 
-L/opt/android/android-ndk-r18b/sources/cxx-stl/llvm-libc++/libs/arm64-v8a
 -lc++ -llog -lz -lm -ldl -lc -lQt5Widgets -lQt5Gui -lQt5Script 
-lQt5ScriptTools -lQt5Core -lGLESv2  
-L/opt/android/android-ndk-r18b/sources/cxx-stl/llvm-libc++/libs/arm64-v8a
 /opt/android/android-ndk-r18b/sources/cxx-stl/llvm-libc++/libs/arm64-v8a/libc++.so.21
 -llog -lz -lm -ldl -lc /opt/android/android-ndk-r18b/toolchains/aarch64-linux-android-4.9/prebuilt/linux-x86_64/lib/gcc/aarch64-linux-android/4.9.x/../../../../aarch64-linux-android/bin/ld:
 cannot find -lc++
clang++: error: linker command failed with exit code 1 (use -v to see invocation)
"Makefile:237: recipe for target 'libcalculator.so' failed"
make: *** [libcalculator.so] Error 1