switch allowing duplicated cases for switch on bit<4>

[apinski-cavium]

Take:

#include <core.p4>

control c(in bit<4> a)
{
  apply {
    switch (a) {
      4w0: {}
      4w1: {} // { dg-note "" }
      4w1: {} // { dg-error "" }
    }
  }
}

control ct(in bit<4> a);
package pt(ct t);
pt(c()) main;

This should fail as 4w1 is repeated. The langauge spec is clear here even:

12.7.3. Notes common to all switch statements
It is a compile-time error if two labels of a switch statement equal each other.