[PATCH v2 00/31] Add a type-safe API to registries

[Tom Tromey]

This is v2 of my series to add a type-safe API to the registry
feature.

v1 was here: https://sourceware.org/ml/gdb-patches/2019-04/msg00436.html

Compared to v1, this version:

* Changes the "emplace" method so that it is only visible when the
  deleter is std::default_deleter.

* Adds a "clear" method to simplify some common code sequences.

* Converts many more (but still not all) modules to use the new API.

Tested by the buildbot.

Tom