CompatHelper: bump compat for LLVM to 7, (keep existing compat)

[github-actions]

This pull request changes the compat entry for the LLVM package from 6 to 6, 7.
This keeps the compat entries for earlier versions.

Note: I have not tested your package with this new compat entry.
It is your responsibility to make sure that your package tests pass before you merge this pull request.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.31%. Comparing base (dfbc287) to head (f339f1e).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #435   +/-   ##
=======================================
  Coverage   80.31%   80.31%           
=======================================
  Files          45       45           
  Lines        2596     2596           
=======================================
  Hits         2085     2085           
  Misses        511      511           

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