fix C compilation warning about function prototype in __SET_EXTERNAL

Example warning:
./POUS.c:1220:3: error: function declaration isn't a prototype [-Werror=strict-prototypes]
__SET_EXTERNAL(data__->,KN_AUT,,__GET_VAR(data__->KEY_AUT.STATE_OUT));
^
compilation terminated due to -Wfatal-errors.
cc1: all warnings being treated as errors

fix C compilation warning from gcc about /* inside of comment section.


./beremiz/iec_std_lib.h:240:1: error: "/*" within comment [-Werror=comment]
/*
^
compilation terminated due to -Wfatal-errors.
cc1: all warnings being treated as errors

Update README.build file with instructions for crosscompiling to win32

Delete commented out code.

Fix FB calls in IL (FB variable name was showing up extraneously before the C function that initializes the POU containing the FB call)

Delete unused code.

Add check for repeated elements in a CASE statement. Emit warnings (and not errors) if found.