fix(build): ensure zero-init of padding bits with GCC 15+

GCC 15 introduces a regression in guaranteed zero-initialization of
padding bits. The suggested solution is to add the
-fzero-init-padding-bits=unions compile option.

To prevent similar issues in the future, this change adds the
-fzero-init-padding-bits=all build option. It ensures that padding bits
in unions and structs are properly zeroed, avoiding regressions.

CMakeLists.txt

@@ -169,6 +169,10 @@ if(CONFIG_COMPILER_DUMP_RTL_FILES)
     list(APPEND compile_options "-fdump-rtl-expand")
 endif()
 
+if(CMAKE_C_COMPILER_ID MATCHES "GNU" AND CMAKE_C_COMPILER_VERSION VERSION_GREATER 15.0)
+    list(APPEND c_compile_options "-fzero-init-padding-bits=all")
+endif()
+
 __generate_prefix_map(prefix_map_compile_options)
 list(APPEND compile_options ${prefix_map_compile_options})