glsl: Don't trust loop analysis in the presence of function calls.

glsl: Don't trust loop analysis in the presence of function calls.

Function calls may have side effects that alter variables used inside
the loop.  In the fragment shader, they may even terminate the shader.
This means our analysis about loop-constant or induction variables may
be completely wrong.

In general it's impossible to determine whether they actually do or not
(due to the halting problem), so we'd need to perform conservative
static analysis.  For now, it's not worth the complexity: most functions
will be inlined, at which point we can unroll them successfully.

Fixes Piglit tests:
- shaders/glsl-fs-unroll-out-param
- shaders/glsl-fs-unroll-side-effect

NOTE: This is a candidate for release branches.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>