[clang] [clang-tools-extra] [llvm] [clang] Introduce diagnostics suppression mappings (PR #112517)

[Aaron Ballman via cfe-commits]

================
@@ -835,4 +835,7 @@ def err_drv_triple_version_invalid : Error<
 
 def warn_missing_include_dirs : Warning<
   "no such include directory: '%0'">, InGroup<MissingIncludeDirs>, DefaultIgnore;
+
+def err_drv_malformed_warning_suppression_mapping : Error<
+  "failed to process suppression mapping file '%0' : %1">;
----------------
AaronBallman wrote:

```suggestion
  "failed to process suppression mapping file '%0': %1">;
```
Note: we should transition this to using `%select` at some point; passing in arbitrary strings makes it harder for us to localize diagnostic messages properly.

https://github.com/llvm/llvm-project/pull/112517