CMake: Add some warning flags for clang 13 or newer

Same as Autoconf.

This is a follow-up to 54974c9.

Author: fxlb

CMakeLists.txt

@@ -1204,6 +1204,7 @@ if(EXISTS ${CMAKE_SOURCE_DIR}/.devel OR EXISTS ${CMAKE_BINARY_DIR}/.devel)
         check_and_add_compiler_option(-Wcomma)
         check_and_add_compiler_option(-Wmissing-prototypes)
         check_and_add_compiler_option(-Wmissing-variable-declarations)
+        check_and_add_compiler_option(-Wnull-pointer-subtraction)
         check_and_add_compiler_option(-Wold-style-definition)
         if(NOT CMAKE_C_COMPILER_ID MATCHES "Sun")
             # In Sun C versions that implement GCC compatibility "-Wpedantic"
@@ -1219,6 +1220,8 @@ if(EXISTS ${CMAKE_SOURCE_DIR}/.devel OR EXISTS ${CMAKE_BINARY_DIR}/.devel)
         check_and_add_compiler_option(-Wstrict-prototypes)
         check_and_add_compiler_option(-Wundef)
         check_and_add_compiler_option(-Wunreachable-code-return)
+        check_and_add_compiler_option(-Wunused-but-set-parameter)
+        check_and_add_compiler_option(-Wunused-but-set-variable)
         check_and_add_compiler_option(-Wused-but-marked-unused)
         check_and_add_compiler_option(-Wwrite-strings)
     endif()