runtime: consistently define fcntl

runtime: consistently define fcntl

Clean up and consolidate on a single consistent definition of fcntl,
which takes three int32 arguments and returns either a positive result
or a negative errno value.

Change-Id: Id9505492712db4b0aab469c6bd15e4fce3c9ff6e
Reviewed-on: https://go-review.googlesource.com/c/go/+/495075
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Michael Pratt <mpratt@google.com>