-if test "x$enable_context" = "xucontext"; then
- AC_CHECK_HEADERS([ucontext.h])
- ac_header=ucontext.h
- as_ac_Header=`echo "ac_cv_header_$ac_header" | $as_tr_sh`
- if test `eval echo '${'$as_ac_Header'}'` = yes; then
+AC_ARG_WITH(context,
+ [ --with-context=[ucontext/pthread] Use either (System V) swapcontext or pthread [[default=auto]].],,
+ with_context=auto)
+
+case $with_context in
+ ucontext) ;;
+ pthread) ;;
+ auto) with_context=ucontext;;
+ *) AC_MSG_ERROR("--with-context must be either ucontext or pthread") ;;
+esac
+
+if test "x$with_context" = "xucontext" ; then
+ if test "x$ac_check_ucontext" = "xyes"; then