* lftp: update from 4.7.5 to 4.7.6
* strace: update from 4.15 to 4.16
* glib: update from 2.50.2 to 2.50.3
* getmail: update from 4.53.0 to 4.54.0
* poppler: update from 0.51.0 to 0.52.0
Let build-package.sh setup the $PREFIX/lib/libstdc++.so symlink
before building any package, to make sure that all C++ applications
link against a fully featured C++ standard library.
Avoid explicitly declaring a dependency on the libgnustl package
since everyone may link against it at will and instead mark it as
essential.
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.