Rather than using `ModuleDecl::isSystemModule()` to determine whether a
module is not a user module, instead check whether the module was
defined adjacent to the compiler or if it's part of the SDK.
If no SDK path was given, then `isSystemModule` is still used as a
fallback.
Resolves rdar://89253201.
These tests were relying on sourcekitd parsing as frontend instead of
using the driver. Update them now to avoid churn when we fix command
line argument parsing in sourcekit.
The changes from clang-importer-sdk to clang-importer-sdk-nosource -I %t
are because clang-importer-sdk implies using -enable-source-import.
Rather than hack them up to use -Xfrontend, it is cleaner to just stop
using source import at all for these tests. Incidentally, this improved
fidelity in a few places. When using the generated swift modules we
also need to pass a target triple to sourcekit, which exposed some tests
that had mac-specific data. This is a systemic issue for sourcekit
tests, but for now just make those few specific tests that we had
problems with run only on mac.
The code goes into its own sub-tree under 'tools' but tests go under 'test',
so that running 'check-swift' will also run all the SourceKit tests.
SourceKit is disabled on non-darwin platforms.
