Platform-specific RUN lines in lit tests?

[Robinson, Paul]

> > > - Use a macro for "-x c" / "/TC"  (sounds like an overkill for just one
> > > test?)
> > This seems like an annoying thing to deal with - is it particularly
> > useful to test the clang-cl driver rather than just using the normal
> > clang gcc-like driver?
>
> Currently we have to use clang-cl as the default compiler to build tests 
> since we fall back on a few TUs (most notably gtest).
>
> Also, I'd argue that a significant (prevailing?) portion of the ASan users 
> on Windows will use clang-cl driver, so we want it to have the first-class 
> support and test coverage.

Are these hacks specific to ASan or more general?
"hosted on Windows" != "using clang-cl driver"
(not for us, anyway, and we have no plan to switch to clang-cl)
--paulr