Fixed compilation problem on windows.


configure.cmake:
  Added test for pthread_attr_getguardsize
include/my_stacktrace.h:
  Define dummy my_init_stacktrace() to allow one to call it without #ifdef HAVE_STACKTRACE
sql/mysqld.cc:
  Move my_setstacksize() to fix compilation problem on windows
  Don't disable core on signal just becasue platform doesn't handle stack trace