chore: disable unused-but-set-variable for clang (#1441)
chore: disable unused-but-set-variable for clang (#1441)

At some point (I believe version 13.0.0?) clang added a warning that
catches variables that were assigned but unused. This version of clang
(or later) is now bundled w/ github's macos images and is causing our
tests to fail in continuous integration. We can currently generate C
code that trips this warning, so for now I've disabled it as we do some
other warnings related to variable usages.
carp-lang/Carp,carp-lang/Carp,carp-lang/Carp