This broke systems where it isn't appropriate to clear the module cache.
The build script already does this when you do a full build; for other
cases, we should just deal with it. (You can still specify a custom
MODULE_CACHE_PATH to make it easier to delete, rather than relying on the
system one.)
This reverts commit r14364.
<rdar://problem/16232176>
Swift SVN r14872
This will catch almost all module cache errors during compiler / stdlib
development, at the cost of slowing down rebuilds of the overlay modules
a bit.
Swift SVN r14364
This ended up being easiest with a runtime function. I couldn't push this
into the standard library because the standard library doesn't know about
NSObject, and I couldn't compile the ObjectiveC module as -parse-stdlib
because it uses standard library types and doesn't otherwise know how to
find the "swift" module.
Swift SVN r7581
