internal/poll: use correct fcntl implementations

Use the libc fcntl (via syscall.fcntl) on aix and solaris like it is
already done for darwin.

For the syscall-based fcntl implementation use FcntlSyscall from
internal/syscall/unix in order to get fcntl64 on 32-bit Linux
systems.

On aix, fcntl with F_DUPFD_CLOEXEC is not supported. Thus, defined
F_DUPFD_CLOEXEC = 0 in the syscall package and check its value before
calling fcntl(fd, syscall.F_DUPFD_CLOEXEC, 0).

On js/wasm, fcntl is not supported thus let its implementation return
ENOSYS directly.

Updates #36211

Change-Id: I96a2ea79e5c4eed2fefd94d0aefd72c940825682
Reviewed-on: https://go-review.googlesource.com/c/go/+/212278


Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>