Created by: dolphin8

many of the CXX_FLAGS are duplicated, e.g. "-march=armv7-a -mfloat-abi=softfp", and some are even conflicted, e.g. "-std=c++11 -O3 -std=c++11", "-std=c++14", "-O2", "-O3".

some CXX_FALGS are defined in CMakeList.txt, and some are in build.sh, while the majority comes from tools/android-cmake/android.toolchain.cmake. It is not easy to change the flags or find out which flag is currently being used.

some work need to be done to uniform the definition of CXX_FLAGS.

/Users/wanghaipeng03/android-ndk-r17/toolchains/llvm/prebuilt/darwin-x86_64/bin/clang++ --target=armv7-none-linux-androideabi --gcc-toolchain=/Users/wanghaipeng03/android-ndk-r17/toolchains/arm-linux-androideabi-4.9/prebuilt/darwin-x86_64 --sysroot=/Users/wanghaipeng03/android-ndk-r17/sysroot -DARMV7 -DBATCHNORM_OP -DBOXCODER_OP -DCONCAT_OP -DCONVADDRELU_OP -DCONV_OP -DDEPTHWISECONV_OP -DELEMENTWISEADD_OP -DENABLE_EXCEPTION -DFUSIONCONVADD_OP -DFUSION_FC_OP -DLRN_OP -DMULTICLASSNMS_OP -DMUL_OP -DPADDLE_MOBILE_DEBUG -DPOOL_OP -DPRIORBOX_OP -DRELU_OP -DRESHAPE_OP -DSIGMOID_OP -DSOFTMAX_OP -DTRANSPOSE_OP -Dpaddle_mobile_EXPORTS -I/Users/wanghaipeng03/github.com/PaddlePaddle/paddle-mobile/src -isystem /Users/wanghaipeng03/android-ndk-r17/sources/cxx-stl/llvm-libc++/include -isystem /Users/wanghaipeng03/android-ndk-r17/sources/android/support/include -isystem /Users/wanghaipeng03/android-ndk-r17/sources/cxx-stl/llvm-libc++abi/include -isystem /Users/wanghaipeng03/android-ndk-r17/sysroot/usr/include/arm-linux-androideabi -D__ANDROID_API__=15 -g -DANDROID -ffunction-sections -funwind-tables -fstack-protector-strong -no-canonical-prefixes -march=armv7-a -mfloat-abi=softfp -mfpu=vfpv3-d16 -fno-integrated-as -mthumb -mfpu=neon -Wa,--noexecstack -Wformat -Werror=format-security -std=c++11 -O3 -std=c++11 -s -march=armv7-a -mfpu=neon -mfloat-abi=softfp -pie -fPIE -w -Wno-error=format-security -llog -std=c++14 -O2 -g -DNDEBUG -fPIC -o CMakeFiles/paddle-mobile.dir/src/operators/kernel/fpga/conv_kernel.cpp.o -c /Users/wanghaipeng03/github.com/PaddlePaddle/paddle-mobile/src/operators/kernel/fpga/conv_kernel.cpp