in order for pthread_cancel to work (which oftpd uses to close inactive
connections), most ports need to load libgcc_s.so.1.  but when oftpd uses
a chroot, that file is no longer available (in fact, it'll try to load it
from the chroot itself which is kind of a security issue).  so have the
code proactively link against libgcc_s when it is found so that the lib
is already loaded when we cancel.

--- a/configure.in
+++ b/configure.in
@@ -39,6 +39,7 @@ AC_FUNC_STRFTIME
 AC_CHECK_FUNCS(getcwd gettimeofday select socket strerror localtime_r gmtime_r)
 dnl AC_CHECK_LIB(pthread, pthread_create)
 dnl AC_SEARCH_LIBS(pthread_create, [ pthread pthreads thread threads ])
+AC_CHECK_LIB(gcc_s, _Unwind_Resume)
 AC_SEARCH_LIBS(socket, socket)
 AC_SEARCH_LIBS(inet_ntoa, nsl)
 AC_CHECK_FUNCS(inet_aton)