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/prog_print.c b/src/mesa/shader/prog_print.c
index 516ea73..80be51c 100644
--- a/src/mesa/shader/prog_print.c
+++ b/src/mesa/shader/prog_print.c
@@ -592,6 +592,8 @@
       default:
          ;
       }
+      if (inst->TexShadow)
+         _mesa_fprintf(f, " SHADOW");
       fprint_comment(f, inst);
       break;