[Bug bootstrap/81037] Xcode 9 requires back ports on gcc-5-branch for bootstrapping under Xcode 9

[howarth.at.gcc at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81037

--- Comment #7 from Jack Howarth <howarth.at.gcc at gmail dot com> ---
Created attachment 42011
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=42011&action=edit
proposed back port of changes from trunk for gcc-5-branch