+AC_CHECK_HEADER(ucontext.h,,, [#include <sys/types.h>])
+AC_CHECK_FUNCS(makecontext swapcontext getcontext setcontext)
+AC_CHECK_MCSC(mcsc=yes, mcsc=no)
+
+dnl # check for pthread method
+AC_CHECK_HEADERS([pthread.h])
+AC_CHECK_LIB(pthread,pthread_create,pthread=yes, pthread=no)
+
+dnl #
+dnl # 2. make a general decision
+dnl #
+
+if test ".$mcsc" = .yes; then
+ mcsc=yes
+elif test ".$pthread" = .yes; then
+ pthread=yes
+else
+ ac_header=windows.h
+ as_ac_Header=`echo "ac_cv_header_$ac_header" | $as_tr_sh`
+ if test `eval echo '${'$as_ac_Header'}'` = yes; then
+ windows_context=yes
+ else
+ AC_ERROR([no appropriate backend found])
+ fi
+fi
+
+dnl #
+dnl # 3. allow decision to be overridden by user
+dnl #
+
+AC_MSG_CHECKING(what kind of backend should we use)