split OP_BR between unconditional & conditional: OP_CBR

split OP_BR between unconditional & conditional: OP_CBR

OP_BR instructions exist in two flavours, relatively much
differentiated: conditional & non-conditional. One has an
operand (and thus its usage need to be cared for, must be
handled in liveness analysis, ..) the other has not; one has
two BB target, the other only one.

There is essentially no places in the code where both flavours
are handled the same. Sometimes they both must be handled but
each with their specificities but in most cases only one of
them is concerned and we need to filter out the other one.
In both cases it means that we need to check what kind we're
dealing with.

There is already a problem with this because there is
several ways to test which kind an OP_BR is and they
are not exactly equivalent:
1) testing if insn->cond is NULL
2) testing if one of insn->bb_true or ->bb_false is NULL.
There exist also an helper (is_branch_goto()) which does
the second tests but which is never used.

It appears that the first test should not be used because
in some cases an conditional OP_BR is changed into
a non-conditional one by (amongst others things) setting
it's ->cond to VOID. We should thus always use the seconds
test (which need two compares with NULL).

This could be corrected in several ways (like changing all
the places wheer the first test is used, use the helper
everywhere or never set ->cond to VOID) but the simplest
is to simply split them in two separated instructions:
OP_BR & OP_CBR, especailly given the fact that in most cases
the OP_BR was first selected by a switch (opcode).

Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Signed-off-by: Christopher Li <sparse@chrisli.org>