[clang-tools-extra] [clang-tidy] Add bugprone-custom-errno-declaration check (PR #213015)

[Csaba Zeitvogel via cfe-commits]

================
@@ -94,32 +194,745 @@ Improvements to clang-query
 Improvements to clang-tidy
 --------------------------
 
+- Improved :program:`check_clang_tidy.py` script by adding the `-check-header`
+  argument to simplify testing of header files. This argument automatically
+  manages the creation of temporary header files and ensures that diagnostics
+  and fixes are verified for the specified headers.
+
+- Improved :program:`clang-tidy` ``-store-check-profile`` by generating valid
+  JSON when the source file path contains characters that require JSON escaping.
+
+- Improved :program:`clang-tidy` by preserving literal backslash characters in
+  POSIX source paths.
+
+- Ensured that :program:`clang-tidy` and the clang compiler uses the same logic
+  for the suppression of compiler diagnostics in system headers and expansions
+  of macros defined in system headers. Previously the default setting of tidy
+  overzealously suppressed some diagnostics that would have been emitted by the
+  compiler. (E.g. tidy suppressed many ``clang-diagnostic-invalid-offsetof``
+  reports because they usually occur in expansion of the macro ``offsetof``.)
+
+- :program:`clang-tidy` will no longer exit immediately if the only enabled
+  checks are `clang-diagnostic-*` ones. This allows using
+  :program:`clang-tidy` purely as a frontend to Clang's builtin warnings.
+
 New checks
 ^^^^^^^^^^
 
-- New :doc:`performance-expensive-value-or
-  <clang-tidy/checks/performance/expensive-value-or>` check.
+- New :doc:`bugprone-assignment-in-selection-statement
+  <clang-tidy/checks/bugprone/assignment-in-selection-statement>` check.
+
+  Finds assignments within selection statements.
+
+- New :doc:`bugprone-cerrno
+  <clang-tidy/checks/bugprone/cerrno>` check.
+
+  Warns if you declare an extern int variable named 'errno'.
----------------
zeitcsabi wrote:

Implemented in [b3fbd08](https://github.com/llvm/llvm-project/pull/213015/changes/b3fbd08ae7cf91e941717a9c96a40aad90d5fd18)

https://github.com/llvm/llvm-project/pull/213015