+m4_warn([obsolete],
+[your code may safely assume C89 semantics that RETSIGTYPE is void.
+Remove this warning and the `AC_CACHE_CHECK' when you adjust the code.])dnl
+AC_CACHE_CHECK([return type of signal handlers],[ac_cv_type_signal],[AC_COMPILE_IFELSE(
+[AC_LANG_PROGRAM([#include <sys/types.h>
+#include <signal.h>
+],
+ [return *(signal (0, 0)) (0) == 1;])],
+ [ac_cv_type_signal=int],
+ [ac_cv_type_signal=void])])
+AC_DEFINE_UNQUOTED([RETSIGTYPE],[$ac_cv_type_signal],[Define as the return type of signal handlers
+ (`int' or `void').])
+