[libiberty patch] Add demangler support for cloned function symbols (PR 40831)

[Cary Coutant]

> OpenMP uses ".omp_fn.n" and ".omp_cpyfn.n" suffixes, see e.g.
> g++ -fopenmp -S libgomp/testsuite/libgomp.c++/task-3.C
> to see both of the types generated by the compiler.
> _Zaaaaa.omp_fn.n is the outlined body of a parallel or task region,
> _Zaaaaa.omp_cpyfn.n is a function to copy over firstprivate classes
> of task regions.

OK, thanks. Dmitry G. also commented that the patch does not work "for
`_Z3fooi.1988' or `_Z3fooi.part.9.165493.constprop.775.31805'."
Apparently, there can be multiple numeric suffixes, and a cloned
function can be cloned again. Is it worth trying to identify the kinds
of cloning in the demangled name, or should I just look for a generic
pattern instead?

-cary