[vpython] replace unix.Syscall with unix.FcntlInt
[vpython] replace unix.Syscall with unix.FcntlInt

This is for
https://chromium-review.googlesource.com/c/infra/infra/+/2387883
that includes change of
https://go.googlesource.com/sys.git/+/6fcdbc0bbc04dcd9e7dc145879ceaf9bf1c6ff03

Change-Id: Icbf8c9196b567a584d35aff06dde1644da93cfb5
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/2389282
Reviewed-by: Vadim Shtayura <9f116ddb1b24f6fc1916a676eb17161b6c07dfc1@chromium.org>
Commit-Queue: Vadim Shtayura <9f116ddb1b24f6fc1916a676eb17161b6c07dfc1@chromium.org>
Commit-Queue: Takuto Ikuta <71927f930fca81015e0f496c65cd126ab1a692e3@chromium.org>
Auto-Submit: Takuto Ikuta <71927f930fca81015e0f496c65cd126ab1a692e3@chromium.org>

luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go