Fix compiling bug in android_armv7_demo : cxx demo can not compile properly...

Fix compiling bug in android_armv7_demo : cxx demo can not compile properly because demo' android version is different from that of library file (#2308)

link armv7 demo to android-23 to make sure the demo can compile properly
cxx demo can not compile properly because demo' android version is different from that of library file, we fix this bug by linking armv7 demo to android-23

lite/demo/cxx/Makefile.def

@@ -26,7 +26,7 @@ else
     CXX_FLAGS = -march=armv7-a -mthumb -mfpu=neon -mfloat-abi=softfp -funwind-tables -no-canonical-prefixes \
 		-D__ANDROID_API__=23 -fexceptions -frtti  -std=c++11 -fopenmp -O3 -DNDEBUG -fPIE
     CXXFLAGS_LINK = $(CXX_FLAGS) -pie -Wl,--fix-cortex-a8 -Wl,--gc-sections -Wl,-z,nocopyreloc
-    SYSROOT_LINK = --sysroot=/opt/android-ndk-r17c/platforms/android-22/arch-arm
+    SYSROOT_LINK = --sysroot=/opt/android-ndk-r17c/platforms/android-23/arch-arm
     SYSTEM_LIBS = /opt/android-ndk-r17c/sources/cxx-stl/llvm-libc++/libs/armeabi-v7a/libc++_static.a \
                   /opt/android-ndk-r17c/sources/cxx-stl/llvm-libc++/libs/armeabi-v7a/libc++abi.a \
                   /opt/android-ndk-r17c/sources/cxx-stl/llvm-libc++/libs/armeabi-v7a/libandroid_support.a \