gdb/python: Reuse gdb.RegisterGroup objects where possible
Only create one gdb.RegisterGroup Python object for each of GDB's
reggroup objects.
I could have added a field into the reggroup object to hold the Python
object pointer for each reggroup, however, as reggroups are never
deleted within GDB, and are global (not per-architecture) a simpler
solution seemed to be just to hold a single global map from reggroup
pointer to a Python object representing the reggroup. Then we can
reuse the objects out of this map.
After this commit it is possible for a user to tell that two
gdb.RegisterGroup objects are now identical when previously they were
unique, however, as both these objects are read-only I don't think
this should be a problem.
There should be no other user visible changes after this commit.
gdb/ChangeLog:
* python/py-registers.c : Add 'unordered_map' include.
(gdbpy_new_reggroup): Renamed to...
(gdbpy_get_reggroup): ...this. Update to only create register
group descriptors when needed.
(gdbpy_reggroup_iter_next): Update.