depend: assume we can always pass '-o' to the C compiler

depend: assume we can always pass '-o' to the C compiler

This is the case after the change in commit v1.13.1-56-g34001a9 of
2013-01-09 (compile: use 'compile' script when "-c -o" is used with
losing compilers).

This is just a simplification; no semantic changes are intended.

* bin/automake.in (handle_languages): Drop transform '%-o%', and
definitions of '$output_flag'.
* lib/am/depend2.am: Adjust to just assume the '?-o?' transform is
true, and the '%-o%' transform expands to "-o".

Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>