This introduces a new method, program_space::remove_objfile, and
changes the objfile destructor not to unlink an objfile from the
program space's list.
This is cleaner because, like the previous patch, it treats the
program space more like a container for objfiles. Also, this makes it
possible to keep an objfile alive even though it has been unlinked
from the program space's list, which is important for processing in a
worker thread.
gdb/ChangeLog
2019-12-12 Tom Tromey <tom@tromey.com>