Add a workaround for a bug in clang-tidy 16 and C++20.

In that mode, the Bazel suppression of a Clang warning doesn't actually
suppress the clang-tidy check. Neither does disabling the check in
a `.clang-tidy` config file. Instead, disable it directly on the command
line when running `clang-tidy`. The clang-tidy bug is:
llvm/llvm-project#61969

This is harmless for other versions as this check is not useful with
most Bazel configurations, and can be achieved with a compiler warning
if truly needed.

Fixes #29

clang_tidy/run_clang_tidy.sh

@@ -25,4 +25,16 @@ test -e .clang-tidy || ln -s -f $CONFIG .clang-tidy
 logfile="$(mktemp)"
 trap 'if (($?)); then cat "$logfile" 1>&2; fi; rm "$logfile"' EXIT
 
+# Prepend a flag-based disabling of a check that has a serious bug in
+# clang-tidy 16 when used with C++20. Bazel always violates this check and the
+# warning is typically disabled, but that warning disablement doesn't work
+# correctly in this circumstance and so we need to disable it at the clang-tidy
+# level both as a check and from `warnings-as-errors` to avoid it getting
+# re-promoted to an error. See the clang-tidy bug here for details:
+# https://github.com/llvm/llvm-project/issues/61969
+set -- \
+  --checks=-clang-diagnostic-builtin-macro-redefined \
+  --warnings-as-errors=-clang-diagnostic-builtin-macro-redefined \
+   "$@"
+
 "${CLANG_TIDY_BIN}" "$@" >"$logfile" 2>&1