This will make things as std::to_string() and other C++ features
work with a modern and supported C++ library.
We package up libc++_shared.so and bump the revision of every C++
using package to make it rebuild against it.
Users who have built C++ using libraries or programs will probably
need to rebuild them if they are linked against Termux-supplied
libraries, as user code was previously linked against gnustl while
the system libraries are now using libc++, and it's not a good idea
to mix C++ standard libraries in a program.
This fixes Android 6 problems (so closes#26).
It also rebuilds termux-elf-cleaner when needed
and bumps some build revisions for packages
needed updates to remove DT_VERDEF and DT_VERDEFNUM.
