Fix linking libuuid on Windows

[hughbe]

We use Windows SDKs to create UUID's (see #5949)

We have to link rpcrt4.lib to get these Win32 APIs - this is available on all Windows PCs.

Extracted from #5904

[compnerd]

This is not globally available. The store partition does not permit it. Can we change the UUID generation to call ::CoCreateGuid instead of CreateUuid? That would link against Ole32.lib instead, and would be more portable across Windows families.

[hughbe]

Hmm, according to the docs, CoCreatsGuid is a kind of wrapper of UUIDCreate:

The CoCreateGuid function calls the RPC function UuidCreate, which creates a GUID, a globally unique 128-bit integer. Use CoCreateGuid when you need an absolutely unique number that you will use as a persistent identifier in a distributed environment.To a very high degree of certainty, this function returns a unique value – no other invocation, on the same or any other system (networked or not), should return the same value.

[compnerd]

Right :) It's merely about Microsoft blessing it for more broad usage.

[hughbe]

Yeah, I was just investigating - I have pushed a change to use ole32.lib, and changed UUIDCreate to CoCreateGuid as you suggested. I've left everything renamed to uuid and used UUID instead of GUID, to simplify the diff. This doesn't matter, as <objbase.h> includes <rpc.h> so these definitions still exist. I think!

[compnerd]

@swift-ci please test and merge

[slavapestov]

@swift-ci Please smoke test

[hughbe]

@slavapestov I'm getting a 404 for one of the test runs: https://ci.swift.org/job/swift-PR-osx/4766/

Seems to be blocking the PR from merging