[clang] [include-cleaner] Support multi-header symbols in mapping generator (PR #147720)

[kadir çetinkaya via cfe-commits]

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@@ -232,4 +247,4 @@ def GetSymbols(parse_pages):
     finally:
         pool.terminate()
         pool.join()
-    return sorted(symbols)
+    return sorted(set(symbols))
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kadircet wrote:

each symbol should already have a unique name, why do we need this conversion to a `set` here?

https://github.com/llvm/llvm-project/pull/147720