I found similar issue https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100570 but it's still even in UNCONFIRMED status - my opinion all just forgot about this issue.
Hello. We use g++ to compile our big project and we use many 3rd party
libraries and frameworks inside(like Qt or Poco). Some of these
frameworks generate many warnings, so we use flag isystem to mark them
as system to suppress 3dparty warnings. But it seems not all warnings
suppressing by this flag. As result we have dozens 3dparty warnings in
our project - they very very garbaging build logs.
