Relax the assumption that at most one Reference-or-Type-like attribute is
present on a DWARF DIE.
Add support for at most one Type attribute (i.e. DW_AT_import xor
DW_AT_type) and separately at most one Reference attribute (i.e.
DW_AT_specification xor DW_AT_abstract_origin xor ...).
Update comment describing old assumption and tag it as a "FIXME" to
reflect the fact that this is perhaps still not general enough.
Add a test based on the case which led me to encounter the bug in the
wild.
Reviewed By: CarlosAlbertoEnciso
Differential Revision: https://reviews.llvm.org/D150713
7f033d0f75