The problem was that when a embedded linked version of mysqltest
crashed there was no way to obtain a stack trace if no core file
is available. Another problem is that the embedded version of
libmysql was not behaving (crash) the same as the non-embedded with
respect to sending commands to a explicitly closed connection.

The solution is to generate a mysqltest's stack trace on crash
and to enable "reconnect" if the connection handle was explicitly
closed so the behavior matches the non-embedded one.

client/CMakeLists.txt:
  Link mysys to mysqltest.
client/Makefile.am:
  Link mysys to mysqltest.
client/mysqltest.c:
  Add fatal signal handling with backtracing for Unix and Windows.
configure.in:
  Add check for weak symbols support and remove a spurious word.
include/Makefile.am:
  Add new header with prototype for stack tracing functions.
include/my_stacktrace.h:
  Add new header with prototype for stack tracing functions.
libmysqld/CMakeLists.txt:
  stack tracing is now part of mysys.
libmysqld/Makefile.am:
  stack tracing is now part of mysys.
libmysqld/lib_sql.cc:
  Re-connect if connection was explicitly closed. This is
  done to match the behavior of the non-embeded libmysql.
mysql-test/t/sql_low_priority_updates_func.test:
  Test expects parallelism between queries that cannot be
  guaranteed under embedded.
mysys/CMakeLists.txt:
  Add stacktrace to mysys.
mysys/Makefile.am:
  Add stacktrace to mysys.
mysys/stacktrace.c:
  Move stacktrace to mysys and add weak symbol for the
  C++ name de-mangling function so that it can later be
  overridden in C++ code. Also add my_ prefix to exported
  functions.
sql/CMakeLists.txt:
  stacktrace was moved to mysys.
sql/Makefile.am:
  stacktrace was moved to mysys.
sql/mysqld.cc:
  Add my_ prefix to mysys functions.