Enable support for data-dependent if-else

[agent-lee]

Needed for catching corner cases regarding pathological values.

Repro specification:

  float acc = 0.0f;
  for (int i = 0; i < 4; i++) {
    acc += a_in[i] * a_in[i];
  }
  for (int i = 0; i < 4; i++) {
    if (acc == 0.0f) {
      b_out[i] = 0.0f;
    } else {
      b_out[i] = a_in[i] / acc;
    }
  }
}```

Compilation aborts with:

Writing intermediate files to: compile-out
==: this match expander must be used inside match
in: (== acc 0.0)
context...:
do-raise-syntax-error
apply-transformer-in-context
apply-transformer52
dispatch-transformer41
for-loop
[repeats 1 more time]
finish-bodys
for-loop
finish-bodys
for-loop
[repeats 1 more time]
finish-bodys
for-loop
[repeats 1 more time]
finish-bodys
for-loop
...
Error: Compilation aborted. cdios return error code 1.

[avanhatt]

The example kernel here is data-dependent, so support will probably involve modifying the rewrite engine and backend in addition to the c frontend.