Because current pragma(msg) behavior is inconsistent with template argument ones.

Template argument accepts three entities - interpreted expressions, types, and symbols. In 2.063 and earlier, pragma(msg) had accepted same entities as its arguments, and print their string representations. However today, pragma(msg) causes errors just only for symbols.
@don-clugston-sociomantic , if you recommend to use `.stringof` for symbols, why not also reject types on pragma(msg) arguments? It sounds not consistent to me.