misra: fix rule 5.4 false positive

[conradoplg]

I apologize if I'm jumping the gun since I'm evaluating cppcheck but I don't have a copy of the MISRA rules yet. But from I've deduced, cppcheck misra.py raises a false positive when a macro is defined "twice" in a #if/#else, e.g.

#ifdef misra_5_4_macro_hides_macro__31x
#define misra_5_4_macro 1 // no warning
#else
#define misra_5_4_macro 2 // no warning
#endif

misra.py thinks these are two distinct macros that have the same 31/63-character prefix, which would violate rule 5.4.

[danmar]

Thanks! I agree, that was a FP.