The previous commit removed the code related to the internal symbol
table.  On platforms where available, we can now use backtrace_symbols()
to print more verbose symbols table to the output.

As there's now general availability of backtrace() and
backtrace_symbols() functions (see below), the commit also removes the
usage of glibc internals and the custom stack tracing.

* backtrace(), backtrace_symbols(), and backtrace_symbols_fd() are
  provided in glibc since version 2.1.
* backtrace(), backtrace_symbols(), and backtrace_symbols_fd() first
  appeared in Mac OS X 10.5.
* The backtrace() library of functions first appeared in NetBSD 7.0 and
  FreeBSD 10.0.