This patch modifies ParseableInterfaceBuilder::CollectDepsForSerialization to
avoid serializing dependencies from the runtime resource path into the
swiftmodules generated from .swiftinterface files. This means the module cache
should now be relocatable across machines.
It also modifies ParseableInterfaceModuleLoader to never add any dependencies
from the module cache and prebuilt cache to the dependency tracker (in addition
to the existing behaviour of not serializing them in the generated
swiftmodules). As a result, CollectDepsForSerialization no longer checks if the
dependencies it is given come from the cache as they are provided by the
dependency tracker. It now asserts that's the case instead.
*Their* dependencies are already being serialized out, so this shouldn't affect
up-to-date-checking except by alowing the regular and prebuilt module caches to
be relocated without invalidating their contents. In the case of the prebuilt
module cache, this gets us closer to supporting relocation across machines.
