We have found out there can be separate declarations (`VarDecl` or
`AccessorDecl`) which are effectively the same (with equal mangled name)
but come from different clang modules. This is the case for example
for glibc constants like `L_SET` that appear in both `SwiftGlibc` and
`CDispatch`.
In this patch, we simply avoid full deduplication in that case by
appending the module name to the trap key for non-swift modules.
A more solid solution should be found in the future.
This should cover `-merge-modules` mode.
Dumping of the configuration to the target files was moved to a
separate pair of header/source files, as now it is also done in
`SwiftOutputRewrite.cpp`.
Previously we were not extracting any `swiftmodule` file that was not
a system or a built-in one. This was done to avoid re-extracting
`swiftmodule` files that were built previously in the same build, but it
turned out to be too eager, as there are legitimate cases where a
non-system, non-built-in precompiled swift module can be used. An
example of that is the `PackageDescription` module used in Swift
Package Manager manifest files (`Package.swift`).
We now relax the test and trigger module extraction on all loaded
modules that do not have source files (we trigger source file extraction
for those). The catch, is that we also create empty trap files for
current output `swiftmodule` files (including possible alias locations
set up by XCode).
This means that if a following extractor run loads a previously built
`swiftmodule` file, although it will trigger module extraction, this
will however be skipped as it will find its target file already present
(this is done via the `TargetFile` semantics).
This replaces numeric tag-based prefixes with the actual tag name.
While this means in general slightly larger trap files, it aids
debugging them for a human.
In the future we can make this conditional on some kind of trap debug
option, but for the moment it does not seem detrimental.
Deduplication of `ConcreteVarDecl` is triggered only if its
`DeclContext` is not local. This avoids a mangled name conflict.
Also added more thourough tests for `ConcreteVarDecl` and `ParamDecl`.
