glsl-1.10: add simple loop unrolling test with loop counter in vec4

This tests whether the loop will unroll if one component of vec4 is used as a loop counter. Similar code can be produced by running C&C3 Tiberium Wars under nine with non-integer hardware and than going through ttn.

It currently fails on vec4 hardware with no loops support like (R3xx and R4xx).

This piglit test was requested by @tarceri in mesa#6371 and hopefully it will help someone to actually improve the NIR unrolling code to handle this.