使用 Android NDK Stand-alone 交叉编译工具

NDK r5 正式支持作为独立的交叉编译toolchain（不必依靠Android Make 系统），参考android-ndk-r5/docs/STANDALONE-TOOLCHAIN.html
gcc 目录相关选项参考：http://gcc.gnu.org/onlinedocs/gcc/Directory-Options.html
shared library参考：http://ehuss.net/shared/

1: Source Code => Executable Binary
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$ export NDK=$HOME/android/android-ndk-r5
$ export CC=$NDK/toolchains/arm-linux-androideabi-4.4.3/prebuilt/linux-x86/bin/arm-linux-androideabi-gcc
$ export SYSROOT=$NDK/platforms/android-4/arch-arm
$ $CC --sysroot=$SYSROOT -o hello hello.c

关于--sysroot=dir：Use dir as the logical root directory for headers and libraries. For example, if the compiler would normally search for headers in /usr/include and libraries in /usr/lib, it will instead search dir/usr/include and dir/usr/lib

2: Shared Library(.so) 
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$ $CC --sysroot=$SYSROOT -fPIC -c hello_lib.c
$ $CC --sysroot=$SYSROOT -shared -o libhello_lib.so hello_lib.o
$ $CC --sysroot=$SYSROOT -L. -lhello_lib -o hello hello.c

关于-Ldir：Add directory dir to the list of directories to be searched for -l
关于-llibrary：Search the library named library when linking