swift234

[ClangImporter] Force load adapter modules whenever a Clang module is named.

Loading Cocoa (Clang) triggers the loading of several other modules,
including Foundation (Clang). We want to make sure we bring in the adapter
module Foundation (Swift), so loading Cocoa currently triggers a walk of
all imported modules to check for an adapter. The problem is that
Foundation (Swift) contains some eagerly-deserialized decls, which refer
to decls in Foundation (Clang). These decls were not importing correctly
because we hadn't finished loading all the adapters -- specifically, we
hadn't yet loaded ObjectiveC (Swift). This meant SEL was loaded as
swift.COpaquePointer instead of ObjectiveC.ObjCSel.

Now, when Foundation (Swift) asks to load Foundation (Clang), we'll walk
all imported modules under Foundation (Clang) to check for an adapter
before returning, even if Foundation (Clang) is already in our system.
This probably still isn't the best way to deal with this (particularly
since the modules in the subtree will get visited twice), but it ensures
that we've loaded all necessary adapter modules before trying to import
any decls.

TLDR: Importing Cocoa now correctly imports the Swift overlay for the
ObjectiveC module, meaning SELs are correctly imported.

<rdar://problem/14759044>

Swift SVN r7293