syscall: emulate Flock on AIX
syscall: emulate Flock on AIX

Change-Id: Id8749283407565a497ddb79737e9bf7051a0deac
Reviewed-on: https://go-review.googlesource.com/79095
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

golang/gofrontend,golang/gofrontend,golang/gofrontend,golang/gofrontend