FPHSA: detect inclusion between find modules
Various find modules include each other to delegate finding some subset
or variant of the package. Ideally, these would use find_dependency
or
some other actual find_package
mechanism, but that is a larger change.
Instead, just detect inclusion and suppress FPHSA name mismatch
warnings.
Fixes: #21060 (closed)
Cc: @LoganBarnes
Backport: release