[PATCH 0/8] Add -Wshadow=local

[Tom Tromey <tom@tromey.com>]

This series enables -Wshadow=local for gdb.

I think that shadowing is mildly confusing, and I normally try to
avoid it.  However, for a long time, it wasn't feasible to enable any
shadowing warnings, because gcc would warn about shadowing that was
"uninteresting" -- the classic example being the use of a local
variable named "index".

In this series I chose to use -Wshadow=local, to forbid shadowing
within a function.  -Wshadow=compatible-local is another choice, but I
think that the stated semantics:

    In C++, type compatibility here means the type of the shadowing
    variable can be converted to that of the shadowed variable.

... is maybe insufficient.  For example a situation where the two
different types are both convertible to a third type could be enough
to cause a bug.  That's a bit of a reach maybe, but it seemed to me
that it's not such a big deal, and certainly always safer, to just
disallow shadowing entirely.

Adding this warning found a few latent bugs in gdb.

Regression tested by the buildbot.  Thanks, Sergio, for your work
running this -- it is a great service.

Let me know what you think.  I feel that a change like this should
involve some feedback.

Tom