cmd/cgo: simplify switch statement to if statement

Change-Id: Ie7dce45d554fde69d682680f55abba6a7fc55036
Reviewed-on: https://go-review.googlesource.com/c/142017Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/cgo/gcc.go

@@ -1026,8 +1026,7 @@ func (p *Package) hasSideEffects(f *File, x ast.Expr) bool {
 	found := false
 	f.walk(x, ctxExpr,
 		func(f *File, x interface{}, context astContext) {
-			switch x.(type) {
-			case *ast.CallExpr:
+			if _, ok := x.(*ast.CallExpr); ok {
 				found = true
 			}
 		})
@@ -1276,8 +1275,7 @@ func (p *Package) rewriteRef(f *File) {
 		// in case expression being replaced is first on line.
 		// See golang.org/issue/6563.
 		pos := (*r.Expr).Pos()
-		switch x := expr.(type) {
-		case *ast.Ident:
+		if x, ok := expr.(*ast.Ident); ok {
 			expr = &ast.Ident{NamePos: pos, Name: x.Name}
 		}