[clang-tools-extra] [clang-include-cleaner] Fix incorrect directory issue for writing files (PR #111375)

[kadir çetinkaya via cfe-commits]

================
@@ -173,6 +173,7 @@ class Action : public clang::ASTFrontendAction {
     if (!HTMLReportPath.empty())
       writeHTML();
 
+    // Source File's path relative to compilation database.
     llvm::StringRef Path =
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kadircet wrote:

can we keep reporting with abs-paths here, i.e:
```
llvm::SmallString<256> AbsPath(SM.getFileEntryRefForID(SM.getMainFileID())->getName());
SM.getFileManager().makeAbsolutePath(AbsPath);
...
```

This way we can recognize these paths in main and perform the mapping accordingly.

https://github.com/llvm/llvm-project/pull/111375