Check VAR_EXTERN variables declared in FBs instantiated in a Program (and recursively too - FBs in FBs).
include ../../common.mk
lib_LIBRARIES = libstage4_c.a
libstage4_c_a_SOURCES = generate_c.cc
libstage4_c_a_LIBADD = ../stage4.o
libstage4_c_a_CPPFLAGS = -I../../../absyntax