fix(cmakev2): add --cref with MAPFILE_TARGET and remove global -Wl,--cref

When MAPFILE_TARGET is used in idf_build_executable, add the linker
--cref option so the cross-reference table is written to the map file
instead of stdout. Remove the global -Wl,--cref from default link
options in project.cmake so cref is only applied where a map file
is requested.

tools/cmakev2/build.cmake

@@ -597,6 +597,8 @@ function(idf_build_executable executable)
     if(ARG_MAPFILE_TARGET AND "${linker_type}" STREQUAL "GNU")
         set(mapfile "${CMAKE_BINARY_DIR}/${ARG_NAME}.map")
         target_link_options(${executable} PRIVATE "LINKER:--Map=${mapfile}")
+        # Add cross-reference table to the map file
+        target_link_options(${executable} PRIVATE "LINKER:--cref")
         add_custom_command(
             OUTPUT "${mapfile}"
             DEPENDS ${executable}