SILOptimizer: avoid use-after-free with the name

[compnerd]

On Windows at least, the std::string associated with the name of the
property would be copy constructed before being passed to the diagnostic
engine. The resultant DiagnosticArgument in the InFlightDiagnostic
would hold a StringRef to the copy-constructed std::string. However,
because the arguments are inalloca'ed on Windows, the copy constructed
string would be destructed before the return of the argument.
Fortunately, this would result in the standard library overwriting the
string and the use-after-free would fail to print the argument.
Explicitly construct the StringRef before passing the name to the
diagnostic to avoid the use-after-free.

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

Resolves SR-NNNN.

[compnerd]

CC: @gottesmm

[compnerd]

@swift-ci please test

[gottesmm]

LGTM.

You seem to be finding a bunch of these. Is there a way we could statically define this away?

[compnerd]

I tried to do some trickery with the template specialization, unfortunately, I couldn't find a way to actually do that due to the implicit conversion operator defined for std::string to StringRef. That is what is biting us. I think that we are just getting lucky on other targets.

[jrose-apple]

This can't possibly be the right fix. We pass std::strings to diagnostics all the time. If we're accidentally copying them, that's a problem with the diagnose wrapper, not with the call sites.