swift234

[frontend] Move options for controlling the behavior of the Clang importer into a new ClangImporterOptions class.

Added a new ClangImporterOptions class which wraps the ModuleCachePath and ExtraArgs for the Clang importer.
Added a new ParseClangImporterArgs static function which fills in the passed-in ClangImporterOptions.
Updated CompilerInvocation and CompilerInvocation::parseArgs() to use ClangImporterOptions and ParseClangImporterArgs, respectively.

Swift SVN r11180