On crashes generate a user-friendly resolved and demangled stack
trace when libc provides the necessary functions (newer libc on i386,
x86_64, powerpc, ia64, alpha and s390). Otherwise print a numeric
stack trace as before, relying on resolve_stack_dump utility.


configure.in:
  Add check for backtrace headers, backtrace functions and if
  __cxa_demangle (libstdc++) is available at link time.
sql/mysqld.cc:
  Print the value of the THD::killed variable when dumping. In
  some circumstances knowing if the thread was killed makes
  debugging easier.
sql/stacktrace.c:
  Use the glibc backtrace function when available and demangle
  C++ function names if the __cxa_demangle function is available.
sql/stacktrace.h:
  Locally export and wrap in C linkage the C++ function __cxa_demangle
  if available.