mesa: add TexShadow field to prog_instruction

If the instruction is TEX/TXP/TXL/etc the TexShadow field will be true if
the instruction is a texture fetch with shadow compare.
diff --git a/src/mesa/shader/arbprogparse.c b/src/mesa/shader/arbprogparse.c
index 2e0fc36..62edb7f 100644
--- a/src/mesa/shader/arbprogparse.c
+++ b/src/mesa/shader/arbprogparse.c
@@ -3104,6 +3104,9 @@
                break;
          }
 
+         if (shadow_tex)
+            fp->TexShadow = 1;
+
          /* Don't test the first time a particular sampler is seen.  Each time
           * after that, make sure the shadow state is the same.
           */