Changelog r13 beta2

Changelog

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For Android Studio issues, follow the docs on the Android Studio site.

GCC is no longer supported. It will not be removed from the NDK just yet, but is no longer receiving backports. It cannot be removed until after libc++ has become stable enough to be the default, as some parts of gnustl are still incompatible with Clang. It will likely be removed after that point.

NDK_TOOLCHAIN_VERSION now defaults to Clang.
libc++ has been updated to r263688.
- We've reset to a (nearly) clean upstream. This should remove a number of bugs, but we still need to clean up libandroid_support before we will recommend it as the default.
make-standalone-toolchain.sh is now simply a wrapper around the Python version of the tool. There are a few behavioral differences. See https://android-review.googlesource.com/#/c/245453/
Some libraries for unsupported ABIs have been removed (mips64r2, mips32r6, mips32r2, and x32). There might still be some stragglers.
Issues with crtbegin_static.o that resulted in missing atexit at link time when building a static executable for ARM android-21+ have been resolved: https://github.com/android-ndk/ndk/issues/132
Added CMake toolchain file in build/cmake/android.toolchain.cmake.

This is not intended to be a comprehensive list of all outstanding bugs.
Standlone toolchains using libc++ and GCC do not work. This seems to be a bug in GCC. See the following commit message for more details: https://android-review.googlesource.com/#/c/247498
x86 ASAN still doesn't work. See discussion on https://android-review.googlesource.com/#/c/186276/
Exception unwinding with c++_shared still does not work for ARM on Gingerbread or Ice Cream Sandwich.
Bionic headers and libraries for Marshmallow and N are not yet exposed despite the presence of android-24. Those platforms are still the Lollipop headers and libraries (not a regression from r11).
RenderScript tools are not present (not a regression from r11): https://github.com/android-ndk/ndk/issues/7.