cmd/internal/gc/big: gofmt vendored code

Change-Id: I035e6f1cd159644db5eeef83056b9c34c401e60f
Reviewed-on: https://go-review.googlesource.com/8441Reviewed-by: Robert Griesemer <gri@golang.org>

src/cmd/internal/gc/big/arith_decl.go

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-
-
 package big
 
 func mulWW(x, y Word) (z1, z0 Word) {

src/cmd/internal/gc/big/vendor.bash

@@ -18,5 +18,8 @@ cp $BIGDIR/*.go .
 sed 's/^\/\/ \+build math_big_pure_go$//' arith_decl_pure.go > arith_decl.go
 rm arith_decl_pure.go
 
+# gofmt to clean up after sed
+gofmt -w .
+
 # Test that it works
 go test -short