inst,ir: cancelling inputs (#92)

Adds support for a `CancellingInputs` instruction flag, to indicate cases like `XORQ R10, R10` where the instruction actually does not depend on the value of `R10` at all.

Closes #89

internal/gen/godata.go

@@ -57,6 +57,10 @@ func (g *godata) Generate(is []inst.Instruction) ([]byte, error) {
 				g.Printf("},\n")
 			}
 
+			if f.CancellingInputs {
+				g.Printf("CancellingInputs: true,\n")
+			}
+
 			g.Printf("},\n")
 		}
 		g.Printf("},\n")