libgo: fix bad value for O_CLOEXEC on AIX 7.1

On AIX 7.1, O_CLOEXEC is defined as 0x0000001000000000, which
creates an integer constant overflow error when building libgo.

This affects only 7.1, O_CLOEXEC is not defined on 6.1 (and
defaults to O in sysinfo.go) and is defined as 0x00800000 on
AIX 7.2.

Issue golang/go#19200

Change-Id: If882b0cbc72426e623e8b735100d232d1b1e7c69
Reviewed-on: https://go-review.googlesource.com/41214
Reviewed-by: Ian Lance Taylor <iant@golang.org>
4 files changed