build-sys: check and bail out for explicitly detected missing [f]lex.

diff --git a/configure.ac b/configure.ac
index e31240c..305508f 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -47,6 +47,9 @@ AC_SUBST(LEXLIB)
 # Check that we have flex/bison and not lex/yacc.
 AC_MSG_CHECKING([for flex vs. lex])
 case $LEX in
+    *missing\ flex*)
+        AC_MSG_ERROR([looks like you're missing flex])
+        ;;
     *flex*)
         AC_MSG_RESULT([ok, looks like we have flex])
         ;;