[ dev-libs/libdwarf ] : add dwarf library for gentoo-zh

libdwarf is a library and a set of tools for reading and writing DWARF2 and later debugging information.
I got the ebuild from [here](http://gpo.zugaina.org/dev-libs/libdwarf)
the libdwarf's [homepage](https://github.com/Distrotech/libdwarf)