Reorganize definition of languages

Reorganize definition of languages

* lib/autoconf/c.m4 (AC_LANG(C), AC_LANG(C++), AC_LANG(Objective C),
_AC_LANG_ABBREV(C), _AC_LANG_ABBREV(C++), _AC_LANG_ABBREV(Objective C),
_AC_LANG_PREFIX(C), _AC_LANG_PREFIX(C++), _AC_LANG_PREFIX(Objective C)):
Replace definitions with usage of AC_LANG_DEFINE.
(Sections 2b, 2c): Delete.
(Sections 1b, 1c): Move after section 2a.
* lib/autoconf/erlang.m4 (AC_LANG(Erlang), _AC_LANG_ABBREV(Erlang),
_AC_LANG_PREFIX(Erlang), AC_LANG_SOURCE(Erlang)): Replace definitions
with usage of AC_LANG_DEFINE.
(AC_LANG_ERLANG): Define using AU_DEFUN.
* lib/autoconf/fortran.m4 (AC_LANG(Fortran), AC_LANG(Fortran 77),
_AC_LANG_ABBREV(Fortran), _AC_LANG_ABBREV(Fortran 77),
_AC_LANG_PREFIX(Fortran), _AC_LANG_PREFIX(Fortran 77),
_AC_LANG_SOURCE(Fortran), AC_LANG_SOURCE(Fortran 77)): Replace
definitions with usage of AC_LANG_DEFINE.
* lib/autoconf/lang.m4 (AC_LANG_DEFINE, AC_LANG_SOURCE()): New.