[Bug lto/77821] New: C++ binary size increase or LTO not working?

[tulipawn at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77821

            Bug ID: 77821
           Summary: C++ binary size increase or LTO not working?
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: lto
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tulipawn at gmail dot com
  Target Milestone: ---

I've just revisited the compilation from issue #69082 and all's fine and good
but I can't seem to produce a similarly sized binary as in the past:

$ du -h ufo-gcc*
1716    ufo-gcc4.9-lto
2404    ufo-gcc4.9-nonlto
2384    ufo-gcc6-lto?
2348    ufo-gcc7-lto?
2340    ufo-gcc7-nonlto

In case it's simply about LTO not being used, the regular code is actually
getting smaller. 
For 4.9 it was enough to put `-flto` among C(XX)FLAGS but now, also passing
those as LDFLAGS to the latter gcc's doesn't help. What gives?