glsl: check if induction var incremented before use in terminator

glsl: check if induction var incremented before use in terminator

do-while loops can increment the starting value before the
condition is checked. e.g.

  do {
    ndx++;
  } while (ndx < 3);

This commit changes the code to detect this and reduces the
iteration count by 1 if found.

V2: fix terminator spelling

Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>
Reviewed-by: Elie Tournier <elie.tournier@collabora.com>
Tested-by: Dieter Nützel <Dieter@nuetzel-hh.de>