Parse function name from DWARF DW_AT_abstract_origin

A DW_TAG_subprogram entry can contain a reference to a
DW_AT_abstract_origin entry instead of duplicating the information
from it (e.g.: name) when the same function is inlined in some case
and not inlined in other cases.

This CL fixes name parsing for the case when the DW_TAG_subprogram
for the non inlined version contains just a reference to the
DW_AT_abstract_origin entry instead of the full information.

Differential revision: http://reviews.llvm.org/D10034

llvm-svn: 238307