Add project-wide .clang-tidy configuration

Introduce a .clang-tidy file to provide consistent code quality checks
across the project.

The configuration is not integrated into .pre-commit-config.yaml because
it depends on a recently generated compile_commands.json file.

Example usage:

	clang-tidy --fix-errors **/*.[ch]

Note: Running clang-tidy should be considered optional, not enforced.

Reviewed-by: Jan Höppner <hoeppner@linux.ibm.com>
Signed-off-by: Jan Polensky <japo@linux.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>

.clang-tidy

@@ -0,0 +1,36 @@
+Checks: >
+  bugprone-*,
+  clang-analyzer-*,
+  misc-*,
+  performance-*,
+  portability-*,
+  readability-*,
+  -bugprone-easily-swappable-parameters,
+  -misc-include-cleaner,
+  -readability-braces-around-statements,
+  -readability-identifier-length,
+  -modernize-*,
+  -performance-*,
+  -portability-*,
+  -readability-implicit-bool-conversion
+
+CheckOptions:
+  - key:             readability-identifier-naming.VariableCase
+    value:           lower_case
+  - key:             readability-identifier-naming.FunctionCase
+    value:           lower_case
+  - key:             readability-identifier-naming.StructCase
+    value:           lower_case
+  - key:             readability-identifier-naming.EnumCase
+    value:           lower_case
+  - key:             readability-identifier-naming.EnumConstantCase
+    value:           UPPER_CASE
+  - key:             readability-identifier-naming.MacroDefinitionCase
+    value:           UPPER_CASE
+  - key:             bugprone-sizeof-expression.WarnOnSizeOfPointer
+    value:           true
+  - key:             misc-unused-parameters.StrictMode
+    value:           true
+
+FormatStyle: file
+UseColor: true