[PATCH] PR libstdc++/13045 / C++ demangler, floating values and function pointer type return type postfix fix.

[DJ Delorie]

> is the most logical thing to do: keep the mangling *exactly* as
> whatever was typed by the programmer.

The mangled name has to be (1) a legal assembler/linker symbol, and
(2) compatible with the rest of the mangling ABI.  Thus, we can't
allow '.' or '+' in the mangled name, nor 'E' (as in 1E4).