Fix autoconf obsolete macros
autogen.sh is reporting some warnings as below
./autogen.sh 2>&1 |grep "obsolete"
libtoolize: copying file 'm4/lt~obsolete.m4'
configure.ac:115: warning: The macro `AC_LANG_C' is obsolete.
configure.ac:115: warning: The macro `AC_TRY_COMPILE' is obsolete.
configure.ac:134: warning: The macro `AC_LANG_C' is obsolete.
configure.ac:134: warning: The macro `AC_TRY_COMPILE' is obsolete.
configure.ac:135: warning: The macro `AC_LANG_C' is obsolete.
configure.ac:135: warning: The macro `AC_TRY_COMPILE' is obsolete.
configure.ac:146: warning: The macro `AC_LANG_C' is obsolete.
configure.ac:146: warning: The macro `AC_TRY_COMPILE' is obsolete.
configure.ac:146: warning: The macro `AC_LANG_C' is obsolete.
configure.ac:146: warning: The macro `AC_TRY_COMPILE' is obsolete.
configure.ac:373: warning: The macro `AC_LANG_C' is obsolete.
configure.ac:373: warning: The macro `AC_TRY_COMPILE' is obsolete.
configure.ac:458: warning: The macro `AC_HEADER_TIME' is obsolete.
configure.ac:681: warning: The macro `AC_TRY_LINK' is obsolete.
configure.ac:807: warning: The macro `AC_TRY_LINK' is obsolete.
As the minimum autoconf version required is v2.69,
we need to make sure to update obsolete macros as described at
https://www.gnu.org/software/autoconf/manual/autoconf-2.69/html_node/Obsolete-Macros.html