Fixed link failure if GTK debugger is present, but no other Bochs facilty
using the pthreads library (SF patch #531 by Dawn Teschendorf fixing SF bug
#1364).


git-svn-id: svn://svn.code.sf.net/p/bochs/code/trunk@12572 6c8e4198-a580-4521-a02f-c9ae86df1db9