[PATCH v3 0/4] diagnostics: libcpp: Overhaul locations for _Pragma tokens

[Lewis Hyatt <lhyatt@gmail.com>]

Hello-

This is an update to the v2 patch series last sent in January:
https://gcc.gnu.org/pipermail/gcc-patches/2023-January/609473.html

While I did not receive any feedback on the v2 patches yet, they did need some
rebasing on top of other recent commits to input.cc, so I thought it would be
helpful to send them again now. The patches have not otherwise changed from
v2, and the above-linked message explains how all the patches fit in with the
original v1 series sent last November.

Dave, I would appreciate it very much if you could please let me know what you
think of this approach? I feel like the diagnostics we currently
output for _Pragmas are worth improving. As a reminder, say for this example:

=====
 #define S "GCC diagnostic ignored \"oops"
 _Pragma(S)
=====

We currently output:

=====
file.cpp:2:24: warning: missing terminating " character
    2 | _Pragma(S)
      |                        ^
=====

While after these patches, we would output:

======
<generated>:1:24: warning: missing terminating " character
    1 | GCC diagnostic ignored "oops
      |                        ^
file.cpp:2:1: note: in <_Pragma directive>
    2 | _Pragma(S)
      | ^~~~~~~
======

Thanks!

-Lewis