However, this doesn’t help with the case where gcc-toolchain is
installed in a profile.


Libcpp does have a file canonicalization method, enabled by default (see
--enable-canonical-system-headers.)  Specifically, in files.c,
‘find_file_in_dir’ does:

    /* We try to canonicalize system headers.  */
    if (CPP_OPTION (pfile, canonical_system_headers) && file->dir->sysp)
      {
        char * canonical_path = maybe_shorter_path (path);

Unfortunately, ‘maybe_shorter_path’ (which calls ‘lrealpath’ from
libiberty) doesn’t seem to be called for libc headers, presumably
because it’s too late: file->dir->sysp is false.


In summary, so far I can only think of half a solution, which is the
‘gcc-toolchain’ fix above.

Thoughts?

Ludo’.