[Bug driver/91352] New: Jobserver detection uses fcntl, which is not available on mingw-w64

[pexu@gcc-bugzilla.mail.kapsi.fi]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91352

            Bug ID: 91352
           Summary: Jobserver detection uses fcntl, which is not available
                    on mingw-w64
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: driver
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pexu@gcc-bugzilla.mail.kapsi.fi
  Target Milestone: ---

Hi.

driver::detect_jobserver() et. al. now use fcntl() and `F_GETFD' to determine
status of a jobserver.

However, this implementation unfortunately breaks mingw-w64 cross compiler
builds, as fcntl() is not available on MinGW.  While `fcntl.h' exists, and is
properly detected by the configure script, it misses many of the POSIX file
control options.  Perhaps a similar check that is currently done for `F_SETLKW'
should be also done for `F_GETFD'.