The old code had overgrown itself and become difficult to read and
modify. I've rewritten it and moved it into its own translation unit.
I moved PreparedActualArgument to the header file for the
transformational intrinsic lowering. Logically, it belongs in
ConvertCall.h, but putting it there would create a circular dependency
between HlfirIntrinsics and ConvertCall.
Sorry, I missed it before and it is probably not that important right now: you may want to guard the file content with ifndef FORTRAN_LOWER_....