When checking semantics of expressions, skip semantic checking of data type definitions
(not yet supported). If we don't skip, all subsequent POUs would not be checked.

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