Fix bug (introduced a few commits ago) when generating SFC actions that are mapped onto variables --> Make generate_sfcdecl_c stateless (i.e. does not depend on order by which it is called).

STD_TEST.st
STD_RESSOURCE.c
LOCATED_VARIABLES.h
POUS.c
test
STD_CONF.c
SFC_TEST.st
test.exe
plc.st
POUS.h
VARIABLES.csv