[6.0🍒] Fallback on swift-frontend -scan-dependencies ... fallback path in case libSwiftScan shared library cannot be loaded.
          #1607
        
          
      
  Add this suggestion to a batch that can be applied as a single commit.
  This suggestion is invalid because no changes were made to the code.
  Suggestions cannot be applied while the pull request is closed.
  Suggestions cannot be applied while viewing a subset of changes.
  Only one suggestion per line can be applied in a batch.
  Add this suggestion to a batch that can be applied as a single commit.
  Applying suggestions on deleted lines is not supported.
  You must change the existing code in this line in order to create a valid suggestion.
  Outdated suggestions cannot be applied.
  This suggestion has been applied or marked resolved.
  Suggestions cannot be applied from pending reviews.
  Suggestions cannot be applied on multi-line comments.
  Suggestions cannot be applied while the pull request is queued to merge.
  Suggestion cannot be applied right now. Please check back later.
  
    
  
    
Cherry-pick of #1601
Explanation: On failure to load
libSwiftScanwhen Explicitly Built Modules are enabled, attempt to run a dependency scan by invokingswift-frontend -scan-dependencies ...on the shell and parsing out the JSON output.Risk: Low. This change affects a code-path that is followed only in the event that the Swift toolchain is not configured with a correctly (as-expected) placed libSwiftScan or the event that there is a code-signing difference between the client process and the libSwiftScan it attempts to load. Previously, in these cases we encountered a hard failure. Now, we will try a best-effort fallback path attempt. Default code-path remains unaffected.
Testing: Test added to the automated test suite.
Reviewed By: @cachemeifyoucan, @owenv
Resolves rdar://127768140