[Bug target/87243] FSF GCC needs to do something special (like using xcrun) on darwin18 to find system headers in SDK

[iains at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87243

--- Comment #9 from Iain Sandoe <iains at gcc dot gnu.org> ---
*** Bug 57753 has been marked as a duplicate of this bug. ***