Renovate configure.ac for compatibility with 2.71

configure.ac

-AC_PREREQ(2.59)
+AC_PREREQ([2.69])
 AC_COPYRIGHT([Copyright (c) 2016 UPLEX - Nils Goroll Systemoptimierung])
-AC_INIT([libvmod-blobdigest], [1.1])
+AC_INIT([libvmod-blobdigest],[1.1])
 AC_CONFIG_MACRO_DIR([m4])
 m4_ifndef([VARNISH_VMOD_INCLUDES], AC_MSG_ERROR([Need varnish.m4 -- see README.rst]))
 AC_CONFIG_SRCDIR(src/vmod_blobdigest.vcc)
-AM_CONFIG_HEADER(config.h)
+AC_CONFIG_HEADERS([config.h])
 
-AC_CANONICAL_SYSTEM
+AC_CANONICAL_TARGET
 AC_LANG(C)
 
 AM_INIT_AUTOMAKE([foreign])
 
-AC_GNU_SOURCE
-AC_PROG_CC
-AC_PROG_CC_STDC
-AC_PROG_CC_C99
-if test "x$ac_cv_prog_cc_c99" = xno; then
-	AC_MSG_ERROR([Could not find a C99 compatible compiler])
-fi
-AC_PROG_CPP
-
 AX_PTHREAD(,[AC_MSG_ERROR([Could not configure pthreads support])])
 
 LIBS="$PTHREAD_LIBS $LIBS"
@@ -28,7 +19,7 @@ CC="$PTHREAD_CC"
 
 LT_INIT([disable-static])
 AC_PROG_INSTALL
-AC_PROG_LIBTOOL
+LT_INIT
 AC_PROG_MAKE_SET
 
 # Check for rst utilities
@@ -38,8 +29,6 @@ if test "x$RST2MAN" = "xno"; then
 fi
 AM_CONDITIONAL(HAVE_RST2MAN, [test "x$RST2MAN" != "xno"])
 
-# Checks for header files.
-AC_HEADER_STDC
 AC_CHECK_HEADERS([sys/types.h])
 AC_CHECK_HEADERS([stdint.h])
 AC_CHECK_HEADERS([unistd.h])