Add pre-commit hook for C code

.pre-commit-config.yaml

@@ -4,6 +4,12 @@
 #
 
 repos:
+  - repo: https://github.com/pre-commit/mirrors-clang-format
+    rev: v19.1.6
+    hooks:
+      - id: clang-format
+        # Exclude the automatically generated file:
+        exclude: ^src/mtime_iso8601\.c$
   - repo: https://github.com/fortran-lang/fprettify
     # We have to use the untagged version because there are no releases that
     # support the case argument in the .fprettify.rc configuration file