Use aarch64-linux-android-4.9 for arm64 build (attempt #4)

GCC: 4.9 (which supports -fstack-protector)
Binutils: 2.24 (which supports gc-sections)
GDB: 7.7

NDK libraries are still picked up from prebuilts/ndk/*/4.8/*

GCC has been patched to disable codegen for calling
__cxa_throw_bad_array_new_length.

Source code has been sync'ed against the 2014-05-14 snapshot which
contains many important fixes (devirtualization, codegen, ...).

Change-Id: I43229360ad0132193d5208cb0d1acba55084853c