Fuzzer action: surround for-loop

[MattWindsor91]

Something like

for (int i = KNOWN_VALUE(x); i <= /* ie iterates once */ atomic_load(x); i++) {
  // surrounded statements go here
}

Depends on #189, and similar to #190 (just changing the < to a <=).

[MattWindsor91]

One issue here is possible overflow of i if known value is, eg, INT_MAX. (Same for #190). This should be feasible to handle eg. by making i go down if known value is positive and up if negative.

[MattWindsor91]

Done a while ago.