c++modules: report imported CMI files as dependencies
They affect the build, so report them via `-MF` mechanisms.
gcc/cp/
* module.cc (do_import): Report imported CMI files as
dependencies.
gcc/testsuite/
* g++.dg/modules/depreport-1_a.C: New test.
* g++.dg/modules/depreport-1_b.C: New test.
* g++.dg/modules/test-depfile.py: New tool for validating depfile
information.
* lib/modules.exp: Support for validating depfile contents.
Signed-off-by: Ben Boeckel <ben.boeckel@kitware.com> Reviewed-by: Jason Merrill <jason@redhat.com>