Clean up handling of Windows RC files

The logic for handling .rc files in Windows has been quite messy. The variable RCFLAGS was incorrectly named RC_FLAGS. In it, we mixed tool-specific values with defines needed by version.rc. The contents of version.rc was needlessly copied in several places, with some variation. Some of the "special" rc files that added to functionality provided by the "global" version.rc was in need of some love.