configure: Fix use of obsolete macros

configure: Fix use of obsolete macros

This fixes the following warnings when using autoconf >= 2.70:

  configure.ac:19: warning: The macro `AC_LANG_C' is obsolete.
  configure.ac:45: warning: The macro `AC_HELP_STRING' is obsolete.
  configure.ac:440: warning: AC_OUTPUT should be used without arguments.

The macros are replacing following the autoconf documentation:

https://www.gnu.org/software/autoconf/manual/autoconf-2.70/html_node/Obsolete-Macros.html

Fixes: https://github.com/bluez/bluez/issues/246
Signed-off-by: Manika Shrivastava <manika.sh@samsung.com>
Signed-off-by: Ayush Garg <ayush.garg@samsung.com>