[NetworkManager-pptp/lr/test] build: deal with some autoconf warnings

[Lubomir Rintel <lkundrak src gnome org>]

commit 94c5271246fdd352125e067c66ebfb18d855933f
Author: Lubomir Rintel <lkundrak v3 sk>
Date:   Mon Jun 27 16:21:01 2022 +0200

    build: deal with some autoconf warnings
    
    The remaining one is about GLIB_GNU_GETTEXT, we'll deal with that in a
    subsequent commit.

 configure.ac | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 715a0d0..b61df11 100644
--- a/configure.ac
+++ b/configure.ac
@@ -12,16 +12,17 @@ AC_CONFIG_MACRO_DIR([m4])
 
 AC_CONFIG_HEADERS([config.h])
 
+AC_USE_SYSTEM_EXTENSIONS
+
 dnl
 dnl Require programs
 dnl
 AC_PROG_CC
 AM_PROG_CC_C_O
 AC_PROG_INSTALL
-AC_PROG_LIBTOOL
+LT_INIT
 AC_PATH_PROG(GLIB_COMPILE_RESOURCES, glib-compile-resources)
 
-AC_GNU_SOURCE
 
 AC_CHECK_PROG([has_file], file, yes, no)
 if test x$has_file = xno ; then
@@ -36,7 +37,6 @@ fi
 dnl
 dnl Required headers
 dnl
-AC_HEADER_STDC
 AC_CHECK_HEADERS(fcntl.h paths.h sys/ioctl.h sys/time.h syslog.h unistd.h)
 
 AC_CHECK_HEADERS(pppd/pppd.h,,
@@ -56,7 +56,6 @@ dnl Checks for typedefs, structures, and compiler characteristics.
 dnl
 AC_TYPE_MODE_T
 AC_TYPE_PID_T
-AC_HEADER_TIME
 
 dnl
 dnl Checks for library functions.