Add object-emission flag for lit tests. This flag is used
to disable following tests for Hexagon that require direct object
generation support.

DebugInfo/dwarf-public-names.ll
DebugInfo/dwarf-version.ll
DebugInfo/member-pointers.ll
DebugInfo/namespace.ll
DebugInfo/two-cus-from-same-file.ll

Fixes bug 15616 - http://llvm.org/bugs/show_bug.cgi?id=15616