objc++: initial support for Objective C++

objc++: initial support for Objective C++

Original thread (dating back to almost three years ago):
<http://lists.gnu.org/archive/html/automake-patches/2009-07/msg00016.html>

* automake.in: Register new language 'objcxx'.
(lang_objcxx_rewrite): New subroutine.
(resolve_linker): Add OBJCXXLINK.
(%_am_macro_for_cond): Add am__fastdepOBJCXX and AC_PROG_OBJCXX.
(%_ac_macro_for_var): Add OBJCXX and OBJCXXFLAGS.
* m4/depend.m4 (_AM_DEPENDENCIES): Add OBJCXX.
* m4/init.m4 (AM_INIT_AUTOMAKE): Add AC_PROG_OBJCXX hook.

Signed-off-by: Peter Breitenlohner <peb@mppmu.mpg.de>
Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>