[Bug c++/43064] improve location and text of diagnostics in constructor initializer lists

[lopezibanez at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=43064

--- Comment #6 from Manuel López-Ibáñez <lopezibanez at gmail dot com> ---
If I remember correctly, the problem here is constants and other
non-expression nodes don't have a location, so diagnostics use
input_location, which points to the end of the initializer. Something like
X+1 should work.

If so, David started fixing this problem, but this code may need fixes
similar to these:  https://gcc.gnu.org/ml/gcc-patches/2018-01/msg00660.html

Otherwise, the problem is more insidious, and the nodes are probably built
with the wrong location.