[llvm] [UpdateTestChecks] Don't fail silently when conflicting CHECK lines means no checks are generated for some functions (PR #159321)

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darker --check --diff -r origin/main...HEAD llvm/utils/UpdateTestChecks/common.py
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``````````diff
--- common.py	2025-09-17 10:58:39.000000 +0000
+++ common.py	2025-09-17 11:08:41.543590 +0000
@@ -953,17 +953,16 @@
 
         for func, warning_info in warnings_to_print.items():
             conflict_strs = []
             for run_index, prefixes in warning_info:
                 conflict_strs.append(
-                    "RUN #{} (prefixes: {})".format(
-                        run_index + 1, ", ".join(prefixes)
-                    )
+                    "RUN #{} (prefixes: {})".format(run_index + 1, ", ".join(prefixes))
                 )
             warn(
                 "For function '{}', the following RUN lines will not generate checks due to conflicting output: {}".format(
-                    func, ", ".join(conflict_strs)),
+                    func, ", ".join(conflict_strs)
+                ),
                 test_file=self._path,
             )
 
         return self._func_dict
 

``````````

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https://github.com/llvm/llvm-project/pull/159321