[Bug target/87243] New: FSF needs to use xcrun on darwin18 to find system headers in SDK

[howarth.at.gcc at gmail dot com]

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

            Bug ID: 87243
           Summary: FSF needs to use xcrun on darwin18 to find system
                    headers in SDK
           Product: gcc
           Version: 9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: howarth.at.gcc at gmail dot com
  Target Milestone: ---

The Xcode 10 release on 10.14 deprecates the presence of the system headers in
/ such that the Command Line Tools package no longer installs a /usr/include
directory. While Apple is providing a fall back header package to install the
SDK in /, this will be dropped in a future macOS release. 

   The Apple clang compilers aren't explicitly patched to address this issue.
Rather the compiler stubs in /usr/bin execute the compilers in the Xcode
application and the Command Line Tools via the xcrun program which sets the
SDKROOT environmental appropriately. Since installing compiler wrappers to do
this for FSF gcc would be problematic for the other targets, the better
approach would be to have the header search path enhanced to default to
-iwithsysroot `xcrun --sdk macosx --show-sdk-path` for FSF gcc.