Android NDK transition to GCC (deprecated) to Clang (recommended)

[danielweck]

Fixed via #240

http://developer.android.com/ndk/downloads/revision_history.html
http://developer.android.com/ndk/guides/application_mk.html
http://developer.android.com/ndk/guides/cpp-support.html#runtimes

https://github.com/readium/readium-sdk/blob/develop/Platform/Android/Application.mk
NDK_TOOLCHAIN_VERSION := 4.9
APP_STL := gnustl_static

=>

NDK_TOOLCHAIN_VERSION := clang3.4
APP_STL := libstdc++

[danielweck]

NDK revision 12:
https://developer.android.com/ndk/downloads/revision_history.html
"The ndk-build command will default to using Clang in an upcoming release. GCC will be removed in a later release."

[danielweck]

See feature branch: https://github.com/readium/readium-sdk/tree/feature/gcc-to-clang
Code diff: develop...feature/gcc-to-clang

[danielweck]

Pull Request: #240