mesa: glsl: re-org of intermediate/temp storage

mesa: glsl: re-org of intermediate/temp storage

Simplify the code for allocating storage for intermediate results.  Use fewer
temps in some cases.

Also, use new asm vec4_move intrinsic instead of regular assigments in various
constructors.  For example:
  float f;
  vec3 v;
  v.xyz = f;
is not legal GLSL, so do this instead:
  __asm vec4_move v.xyz, f;  // note: f will auto-expand into f.xxxx

Plus, fix assorted bugs in structure comparison.