Fix warnings from autoconf by running the autoupdate tool and

adding an argument to AC_PROG_LEX.  The minimum required autoconf
version is set to 2.70 as that was the introduction of the
AC_PROG_LEX argument.

configure.ac

@@ -14,7 +14,7 @@
 # Ensure a recent version of Autoconf is in use
 # Older versions may not work with this script and this will report the
 # problem to the user.
-AC_PREREQ([2.59])
+AC_PREREQ([2.70])
 
 m4_define([ngspice_major_version], [44+])
 m4_define([ngspice_minor_version], [0])
@@ -967,11 +967,12 @@ fi
 # A trivial AC_CHECK_FUNCS(sigsetjmp) won't do because sigsetjmp() might be a
 # macro declared in <setjmp.h>. (joze)
 AC_MSG_CHECKING([for sigsetjmp])
-AC_TRY_LINK([#include <setjmp.h>],[jmp_buf env; sigsetjmp(env, 1);],
-    [AC_MSG_RESULT([yes])
+AC_LINK_IFELSE(
+     [AC_LANG_PROGRAM([[#include <setjmp.h>]],
+                      [[jmp_buf env; sigsetjmp(env, 1);]])],
+     [AC_MSG_RESULT([yes])
         AC_DEFINE([HAVE_SIGSETJMP], [], [Define if we have sigsetjmp().])],
-    [AC_MSG_RESULT([no])])
-
+     [AC_MSG_RESULT([no])])
 
 # Check for the snprintf function:
 AC_CHECK_FUNCS([snprintf])
@@ -1101,7 +1102,7 @@ AC_PATH_PROG([BISON], [bison])
 AX_PROG_BISON_VERSION([2.7], [],
     [AC_DEFINE([OLD_BISON], [], [Bison is older than 2.7]),
      AC_MSG_WARN([Bison is older than 2.7])])
-AC_PROG_LEX
+AC_PROG_LEX(noyywrap)
 
 AM_CONDITIONAL([CMATHTESTS], [test "x$enable_cmathtests" = xyes])
 
@@ -1183,7 +1184,7 @@ if test "x$enable_osdi" = xno; then
     AC_MSG_RESULT([OSDI interface disabled])
 else
     AC_DEFUN([AX_CHECK_COMPILE_FLAG],
-    [AC_PREREQ(2.64)dnl for _AC_LANG_PREFIX and AS_VAR_IF
+    [AC_PREREQ([2.70])dnl for _AC_LANG_PREFIX and AS_VAR_IF
     AS_VAR_PUSHDEF([CACHEVAR],[ax_cv_check_[]_AC_LANG_ABBREV[]flags_$4_$1])dnl
     AC_CACHE_CHECK([whether _AC_LANG compiler accepts $1], CACHEVAR, [
       ax_check_save_flags=$[]_AC_LANG_PREFIX[]FLAGS