[Bug go/67874] New: fd_unix.go does not build when there is fcntl64 and no fcntl syscall

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67874

            Bug ID: 67874
           Summary: fd_unix.go does not build when there is fcntl64 and no
                    fcntl syscall
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: go
          Assignee: ian at airs dot com
          Reporter: pinskia at gcc dot gnu.org
                CC: cmang at google dot com
  Target Milestone: ---
            Target: aarch64-linux-gnu (ilp32)

Since a request from the ARM64 kernel maintainers on the ABI for AARCH64 ILP32
to just use off_t and time_t as 32bit rather than what I originally had it as
64bit, we use the compat syscalls instead which means there is no fcntl syscall
only fcntl64 now.

This breaks building fd_unix.go which depends on SYS_FCNTL being defined but
there is only SYS_FCNTL64 now.