PrivateLibcExtras: Port to Windows

[compnerd]

Replace this paragraph with a description of your changes and rationale. Provide links to external references/discussions if appropriate.

Resolves SR-NNNN.

[jakepetroules]

Wouldn't it make most sense to structure this like:

#if canImport(Darwin)
import Darwin
#elseif os(Windows)
import MSVCRT
import WinSDK
#elseif canImport(Glibc)
import Glibc
#endif

Then things work automatically for other POSIX platforms which probably use Glibc (NetBSD, OpenBSD, etc.?) without needing to explicitly update the list every time someone adds a new OS to Swift.

[compnerd]

This is why I had proposed having a C module which hides this mess. In any case, I suppose that I can change that, but this pattern is prevalent through out the code base. I think it makes sense for someone to go through and catch them all later.

[jrose-apple]

We've talked about such a module before and the primary problem is what to name it. :-) I think there'd be support on -evolution.

[compnerd]

@swift-ci please test

[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - b2dd97143e5e040ed1a40e2e189ac11b10ca7f85

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - b2dd97143e5e040ed1a40e2e189ac11b10ca7f85

[compnerd]

@swift-ci please test

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - b2dd97143e5e040ed1a40e2e189ac11b10ca7f85

[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - b2dd97143e5e040ed1a40e2e189ac11b10ca7f85

[compnerd]

@swift-ci please test

[compnerd]

@jakepetroules - okay, I think that this is good now; it can actually spawn the child and do the appropriate setup in my local testing, the rest of the problem now is in StdlibUnittest. Could you PTAK?

[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - 7e1665d6eaf86e69d21bde52d5f065d6031b2a77

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - 7e1665d6eaf86e69d21bde52d5f065d6031b2a77

out of date, PR updated

[compnerd]

@jrose-apple - anyone else that should take a look at this?

[jrose-apple]

I'd say @moiseev is a good general fallback for anything in stdlib/ (sorry, @moiseev).

(A bunch of this code was written by Dmitri back when he worked on Swift, and of course it was Dmitri so it worked well enough that no one had to update it ever again.)