windows: add Recvfrom and Sendto implementations

[maltalex]

Added the missing Sendto and Recvfrom syscalls for Windows.
Fixes golang/go#7170

[gopherbot]

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Patch Set 1:

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[maltalex]

For your reviewing pleasure, documentation of these syscalls - sendto, recvfrom

[gopherbot]

Message from Ian Lance Taylor:

Patch Set 2: Run-TryBot+1

(2 comments)

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Message from Gobot Gobot:

Patch Set 2:

TryBots beginning. Status page: https://farmer.golang.org/try?commit=10f0a883

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Message from Gobot Gobot:

Patch Set 2: TryBot-Result+1

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[gopherbot]

Message from Alex Maltinsky:

Patch Set 3:

Patch Set 2: Run-TryBot+1

(2 comments)

I missed the part in the contribution guide where it said that the GitHub PR description would become part of the commit message when migrated to Gerrit. The original commit message is a one-liner.

How would I go about changing the commit message here? I'm getting a 403 when I try to edit the commit message in Gerrit.

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Message from Alex Maltinsky:

Patch Set 5:

(2 comments)

Apparently syncing from GitHub just took a while.
The commit message is now fixed.

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[gopherbot]

Message from Ian Lance Taylor:

Patch Set 5: Run-TryBot+1

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Message from Gobot Gobot:

Patch Set 5:

TryBots beginning. Status page: https://farmer.golang.org/try?commit=7975c8cc

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Message from Gobot Gobot:

Patch Set 5: TryBot-Result+1

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[gopherbot]

This PR is being closed because golang.org/cl/208321 has been merged.