Add 'remark' diagnostic type in clang

[Greg Bedwell]

Hi,

> Also, can "remark" diagnostics be upgraded to error or warning by command-line options?

I'm also interested in the answer to this.  The compiler for our other
platforms uses the EDG front-end which, as previously mentioned,
supports the remark level of severity (so I'm personally in favour of
the remark name for diagnostics that are not generally considered
severe enough to be a warning).  Typically our users would
occasionally enable remarks to have a look at what was produced and
often choose to upgrade any that were particularly useful to their
coding style to warnings so that they would be caught by -Werror, etc.
 I don't necessarily think that we have to mimic the EDG behaviour,
but I would like to make sure that we can cover some typical use-cases
when the user interface is designed.

A couple of other things that immediately spring to mind for me in
terms of UI are:

* Using clang from within Visual Studio:  The
-fdiagnostics-format=msvc switch allows errors and warnings to be
parsed correctly by the IDE so that they show up in the Error List
window.  I'm pretty sure that VS doesn't have a concept of remarks so
it won't know to add them to that window, although they obviously will
still be there in the console output.  With EDG, the workaround was
simply to upgrade any remarks you cared about enough to a warning so
they'd show up there.  I don't think this is a big problem, but I
thought I'd throw it out there.

* Currently -Weverything is a really useful feature to immediately see
whether we are capable of producing any diagnostics for a given piece
of code.  Presumably, if we go down the -R... route, I guess we'd need
an equivalent -Reverything switch, and would have to use '-Weverything
-Reverything' instead for that case?

Cheers,
-Greg

--
Greg Bedwell
SN Systems Ltd. - Sony Computer Entertainment Group