Correctly handle structured variables that include FB and external FBs (example: FB1.FB2.extFB3.FB4.extFB5.extFB6.structvar.field1 := 42;) (this commit fixes only ST code. TODO: IL and SFC)

iec.flex.c
iec.y.output
iec.y.cc
iec.y.hh
Makefile.depend