[Bug libbacktrace/88894] New: [libbacktrace] share abbrevs between units

[vries at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88894

            Bug ID: 88894
           Summary: [libbacktrace] share abbrevs between units
           Product: gcc
           Version: 9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libbacktrace
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vries at gcc dot gnu.org
                CC: ian at gcc dot gnu.org
  Target Milestone: ---

For each compilation unit we parse in build_address_map, we call read_abbrevs,
to parse the abbrevs, and store the parsed representation in memory.

However, multiple compilation units can share the same abbrev offset, and in
the current setup we would parse and store such an abbrev twice, which is
inefficient.