Patch for bug c++/17964 (cpp error locations for C++)

[Per Bothner]

Mark Mitchell wrote:
> Joseph S. Myers wrote:
> 
>>This patch fixes bug 17964, a regression in preprocessor diagnostics
>>for C++ caused by lexing up front but deferring string interpretation
>>(which depends on the parse context) until later, so the
>>preprocessor's notion of source location does not relate to the actual
>>source location at that point.
> 
> 
> I think this is fine.
> 
> However, I want to give the cpplib and diagnostic maintainers a chance
> to object.  If there are no objections within 24 hours, please go ahead
> and commit.

No objections from me.

As Joseph points out, things would be simpler/cleaner if
--enable-mapped-location is made the default.  I really could
use some help with this ...
-- 
	--Per Bothner
per@bothner.com   http://per.bothner.com/