Fixed flex version check and support for reentrant parsers.

configure.ac

@@ -22,8 +22,8 @@ LEX_FLEX=`$LEX --version | awk '{print $1;exit}'`
 if test "$LEX_FLEX" != "flex"; then
     AC_MSG_ERROR([GNU flex needed for reentrant parsers, set the \$LEX variable before running configure])
 fi
-if ! $LEX --reentrant </dev/null 2>/dev/null; then
-    AC_MSG_ERROR([GNU flex version 2.X.X or higher needed for reentrant parsers])
+if ! $LEX --reentrant m4/flex-test.l </dev/null 2>/dev/null; then
+    AC_MSG_ERROR([GNU flex version 2.5.33 or higher needed for reentrant parsers])
 fi
 AC_PROG_YACC
 YACC_BISON=`bison --version | awk '{print $1;exit}'`

m4/flex-test.l

+%{
+%}
+
+%option reentrant
+%option bison-bridge
+%option noinput
+%option nounput
+%option noreject
+
+BLANK [ \t\n]
+
+%%
+<<EOF>> return 0;
+%%
+