Handle properly the case of an inlined call that has no abstract origin attribute.

Handle properly the case of an inlined call that has no abstract origin attribute.

Normally, an inlined call has a dwarf entry that points at the abstract origin, i.e. the
function that was inlined.
However, in some cases, the abstract origin tag is not present (observed with gcc 6.3.0, when
compiling with link time optimisation).
Such missing abstract origin was then causing an error message when reading the dwarf debug info.

This patch ensures we handle this case more gracefully, by using UnknownInlinedFun as inlined
function name for such a missing abstract origin;