> +# needs clang-scan-deps, which isn't installed in base.

it shouldn't be needed for ports-gcc archs though; in audio/openal we
did this:

----
# XXX cmake config uses CXX_MODULES, which needs clang-scan-deps
MODULES +=	lang/clang
MODCLANG_COMPILER_LINKS = No

COMPILER =	base-clang ports-gcc
----

it's not perfect as there's an unwanted/unused BDEP on ports-clang on
base-gcc archs, but at least it then should use the same compiler as
most other ports.

(C++20 modules (which need this) are showing up in a few places, I'm
not sure what the cut-off point would be, but it might be worth building
clang-scan-deps in base which would simplify these ports..)