swift234

Generate IR for inline functions from Clang modules.

Currently only inline functions referenced from Swift source files, or
from the REPL, will get IR generated for them. Inline functions
referenced by other inline functions will require additional effort to
generate properly.

With this change we use the clang::CodeGenerator-created llvm::Module
for all IR generation in Swift. This is perhaps undesirable, but
unavoidable given the interface the public Clang APIs expose, which do
not allow for building a ModuleBuilder that borrows an existing
llvm::Module.

Also unfortunate is the hack to generate a UsedAttr for each imported
inline function, but the public Clang APIs do not provide a way to only
emit deferred decls without emitting other things (e.g. module flags
that conflict with what the Swift IRGen emits). Note that we do not do
IRGen for every inline function in the module - only the ones that the
importer pulls in, which appears to be only those transitively
referenced from Swift code.

Swift SVN r13134