[ATFE] Prioritize multilib-specific headers over target-level headers. (#451)

Adjust the header search order so that variant-specific directories (e.g
armv6m_soft_nofp_size/include/) are searched before the common
target-level directories (e.g include/) in the -internal-isystem list.

This ensures that headers tailored for a specific multilib variant take
precedence over the generic headers, allowing correct header resolution
in the presence of overrides.

Previously, the common target-level directory could shadow
multilib-specific headers if the same file existed in both paths.

Author: simpal01

arm-software/embedded/arm-multilib/CMakeLists.txt

@@ -344,8 +344,8 @@ foreach(lib_idx RANGE ${lib_count_dec})
             endforeach()
             if(ENABLE_MULTILIB_HEADER_OPTIMISATION)
                 string(APPEND multilib_yaml_content "  IncludeDirs:\n")
-                string(APPEND multilib_yaml_content "  - ${parent_dir_name}/include\n")
                 string(APPEND multilib_yaml_content "  - ${parent_dir_name}/${variant}/include\n")
+                string(APPEND multilib_yaml_content "  - ${parent_dir_name}/include\n")
             endif()
             string(APPEND multilib_yaml_content "  Group: stdlibs\n")
         else()