When a symbol is GC'd it can still be references by relocations
in the debug sections, but such symbols are not assigned virtual
addresses.
This change adds a new global data symbol which gets GC'd but
should still appears in the output debug info, albeit with a 0
address.
Fixes 37555
Differential Revision: https://reviews.llvm.org/D47238
llvm-svn: 333047
610ac3bd42