Control instruction simplifications

[vouillon]

Some simplifications are possible when compiling Switch (and possibly Cond?).
In particular, one can turn br_table {0} into br 0, and br_table {0, 1, 2} into a conditional.
This could be compiled into a conditional as well:

             br_table {4, 0, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4}