[libcpp] patch: add used callback

[Tom Tromey]

>>>>> "Arnaud" == Arnaud Charlet <charlet@adacore.com> writes:

Arnaud> Here is a submission for a new callback in libcpp that triggers each
Arnaud> time a macro is used (tested or expanded).

To detect when the macro is tested, it seems to me that you would need
calls in directives.c, near the calls to used_define.  Or are you
actually only interested in expansions?

Tom