Enable building with Android API levels longer than one digit
Recognize Android toolchains with 64-bit architectures

This doesn't actually add _support_ for 64-bit architectures; it just allows
building for old architectures with NDK 10+, which includes them.

The bug in the original code was that it lacked an "else" clause, so in
the case of an unknown machine name the architecture name was reused from the
previous iteration. So it could mistakenly assume that aarch64- toolchains
are for the "arm" architecture, with disastrous results.

I removed duplicated logic, added new architecture names and a default case,
as well as tightened the regexes, just in case.
Merge pull request #3434 from SpecLad/new-ndk

Fix android.toolchain.cmake to allow building with new NDKs