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.
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