[PATCH v2] libiberty: fix resource exhaustion in rust demangler (PR demangler/106641)

[Ruslan Valiyev]

Apologies for the bare v2, I hit send before writing the cover note.

To answer your questions: yes, I confirmed GCC PR 106641 is the same
issue (endless loop in demangle_binder from unbounded base-62 lifetime
count, reported in 2022). All references are updated to
PR demangler/106641 in v2.

I don't have write access to GCC or binutils git, so I'd appreciate
it if you could push it.

Thanks,
Ruslan