UTF-8 quotation marks in diagnostics

[Martin Sebor]

> Again, LC_CTYPE does *not* affect source file interpretation.

I understand what you're saying. What I am saying is that if this
is how c99 behaves it's in conflict with POSIX because LC_CTYPE
is exactly how source file interpretation is specified to be
controlled:

   LC_CTYPE
       Determine the locale for the interpretation of sequences of
       bytes of text data as characters (for example, single-byte
       as opposed to multi-byte characters in arguments and input
       files).

> I think we should clearly update the documentation to reflect reality
> regarding source file encoding, and leave it strictly for wrappers such as
> "c99" to specify -finput-charset= options rather than leaving open the
> possibility that GCC's own default might change in future.

That sounds reasonable.

Martin