The code of `ScanDependencies.cpp` was creating invalid JSON since #66031
because in the case of having `extraPcmArgs` and `swiftOverlayDependencies`,
but not `bridgingHeader`, a comma will not be added at the end of
`extraPcmArgs`, creating an invalid JSON file. Additionally that same PR
added a trailing comma at the end of the `swiftOverlayDependencies`, which
valid JSON does not allow, but that bug was removed in #66366.
Both problems are, however, present in the 5.9 branch, because #66936
included #66031, but not #66366.
Besides fixing the problem in `ScanDependencies.cpp` I modified every test
that uses `--scan-dependencies` to pass the produced JSON through
Python's `json.tool` in order to validate proper JSON is produced. In
most cases I was able to pipe the output of the tool into `FileCheck`,
but in some cases the validation is done by itself because the checks
depend on the exact format generated by `--scan-dependencies`. In
a couple of tests I added a call to `FileCheck` that seemed to be
missing.
Without these changes, two tests seems to be generating invalid JSON in
my machine:
- `ScanDependencies/local_cache_consistency.swift` (which outputs `Expecting ',' delimiter: line 525 column 11 (char 22799)`)
- `ScanDependencies/placholder_overlay_deps.swift`
These modules are not guaranteed to be found, which is okay, as compilation is meant to be possible in their absense since their contents are not used in the public API of the module which imports them as implementation-only.
Resolves rdar://103031296
