swift234

Clang importer: use proper Clang context when omitting needless words.

When we're omitting needless words and building Swift name lookup
tables, make sure to use the proper Clang
Sema/Preprocessor/ASTContext. This still needs to be properly
detangled, but at least now we can handle omit-needless-words for
builtin Clang types (e.g., SEL) properly.

As part of this, put OmitNeedlessWords and InferDefaultArguments into
the module file extension hash for the Swift name lookup tables, since
those settings will affect the results.