[clang][deps] Make order of module dependencies deterministic

This fixes the underlying module dependencies, which had a
non-deterministic order, which was also visible in the order of calls to
DependencyConsumer methods. This was not directly observable in
the clang-scan-deps utility, because it was previously seeing a sorted
order from std::map in DependencyScanningTool. However, the underlying
API previously created a likely issue for any other clients. Note: if
you only apply the change from DependencyScanningTool, you can see the
issue in clang-scan-deps, and existing tests will fail
non-deterministicaly.

Differential Revision: https://reviews.llvm.org/D127243