cmd/compile: add rulegen diagnostic

When rulegen complains about a missing type, report the line number
in the rules file.

Change-Id: Ic7c19e1d5f29547911909df5788945848a6080ff
Reviewed-on: https://go-review.googlesource.com/114004Reviewed-by: David Chase <drchase@google.com>

src/cmd/compile/internal/ssa/gen/rulegen.go

@@ -548,7 +548,7 @@ func genResult0(w io.Writer, arch arch, result string, alloc *int, top, move boo
 		}
 	} else {
 		if typ == "" {
-			log.Fatalf("sub-expression %s (op=Op%s%s) must have a type", result, oparch, op.name)
+			log.Fatalf("sub-expression %s (op=Op%s%s) at %s must have a type", result, oparch, op.name, loc)
 		}
 		v = fmt.Sprintf("v%d", *alloc)
 		*alloc++