[PATCH v5 4/5] c++modules: report imported CMI files as dependencies

[Ben Boeckel]

On Mon, Feb 13, 2023 at 13:33:50 -0500, Jason Merrill wrote:
> Both this and the mapper dependency patch seem to cause most of the 
> modules testcases to crash; please remember to run the regression tests 
> (https://gcc.gnu.org/contribute.html#testing)

Fixed for v6. `cpp_get_deps` can return `NULL` which `deps_add_dep`
assumes to not be true; fixed by checking before calling.

--Ben