tools: update list of references to not include symbold used by __assert_func calls

On xtensa architecture, the call to __assert_func uses a reference to __func__ that can
sometimes be placed in flash. Since the __asert_func can be called from functions in IRAM
the check_callgraph script can report an error when checking for invalid calls from IRAM
to flash sections. However, the __asert_func prevents this scenario at runtime so the
check_callgraph script reports a 'flas positive' situation. For this reasson, all references
to __func__$x found prior to a call to __assert_func are droped in the parsing of the rtl files.

components/heap/test_apps/CMakeLists.txt

@@ -13,6 +13,7 @@ if(CONFIG_COMPILER_DUMP_RTL_FILES)
                       find-refs
                       --from-sections=.iram0.text
                       --to-sections=.flash.text,.flash.rodata
+                      --ignore-symbols=__func__/__assert_func,__func__/heap_caps_alloc_failed
                       --exit-code
                       DEPENDS ${elf}
                       )