Add android build script

[lo1ol]

Hi!

I noticed some problems of using my pkcs11 engine with stunnel on android. I'm sure that problem is in -D__ANDROID_API__=14 flag, which you pass to build openssl.

You can't pass ANDROID_API flag lower then ndk least support. New version of SDK uses ANDROID_API=16

I think you should add a public script, which you use to build your android version of openssl and stunnel.

[mtrojnar]

I currently (as of stunnel 5.72) use NDK r24c and:

    API=16
    test -d "$ANDROID_NDK_ROOT" || ANDROID_NDK_ROOT=/usr/lib/android-ndk
    export ANDROID_NDK_ROOT
    TOOLCHAIN=$ANDROID_NDK_ROOT/toolchains/llvm/prebuilt/linux-x86_64
    export TARGET=armv7a-linux-androideabi
    export AR=$TOOLCHAIN/bin/llvm-ar
    export CC=$TOOLCHAIN/bin/$TARGET$API-clang
    export AS=$CC
    export CXX=$TOOLCHAIN/bin/$TARGET$API-clang++
    export LD=$TOOLCHAIN/bin/ld
    export RANLIB=$TOOLCHAIN/bin/llvm-ranlib
    export STRIP=$TOOLCHAIN/bin/llvm-strip
    test -f Makefile && make distclean
    mkdir -p bin/android
    cd bin/android
    ../../configure \
        --with-ssl=$DST \
        --prefix=/data/local/tmp \
        --host=armv7a-linux-androideabi
    make

According to my investigation, NDK r23c is the last version to support API 16.