[Bug c++/93506] Create hybrid of -I and -isystem that is like -I but deactivates warnings

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93506

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2020-01-30
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=70129
     Ever confirmed|0                           |1
           Severity|normal                      |enhancement

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
For example, see PR 70129 where people are having problems because they're
abusing -isystem to get rid of warnings, and that breaks libstdc++ headers.

Rather than yet another -I option (which wouldn't be portable) a better
solution might be a separate option that you use in addition to -I to mark that
path with the "treat as system headers and don't warn"

i.e. -I /some/path -fsystem-headers=/some/path

This assumes that the "it's a system header path" property is a flag that can
be set independently of being in the actual list of system header locations,
rather than just implied.