[DWARFDebugLoc] Tweak error message when resolving offset pairs with no base address

The previous message mentioned DW_LLE_offset_pair, but this is
incorrect/confusing because we can get this message even with DWARF4
(which does not use DW_LLE encodings). This happens because DWARF<=4
location entries are "upgraded" to DWARF v5 during parsing.

The new error message refrains from referencing specific constants.
Fixes pr44482.