build-sys: check and bail out for explicitly detected missing yacc/bison.

diff --git a/configure.ac b/configure.ac
index 305508f..243c9df 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -60,6 +60,9 @@ esac
 
 AC_MSG_CHECKING([for bison vs. yacc])
 case $YACC in
+    *missing\ *)
+        AC_MSG_ERROR([looks like you're missing bison])
+        ;;
     *bison*)
         AC_MSG_RESULT([ok, looks like we have bison])
         ;;