build: use copy for BuildWithResultHandler loop vars

Signed-off-by: Justin Chadwell <me@jedevc.com>
(cherry picked from commit 347417ee12)

build/build.go

@@ -1078,7 +1078,7 @@ func BuildWithResultHandler(ctx context.Context, nodes []builder.Node, opt map[s
 			})
 
 			for i, dp := range dps {
-				so := *dp.so
+				i, dp, so := i, dp, *dp.so
 				if multiDriver {
 					for i, e := range so.Exports {
 						switch e.Type {
@@ -1107,7 +1107,6 @@ func BuildWithResultHandler(ctx context.Context, nodes []builder.Node, opt map[s
 					}
 				}
 
-				func(i int, dp driverPair, so client.SolveOpt) {
 				pw := progress.WithPrefix(w, k, multiTarget)
 
 				c := clients[dp.driverIndex]
@@ -1243,8 +1242,6 @@ func BuildWithResultHandler(ctx context.Context, nodes []builder.Node, opt map[s
 					}
 					return nil
 				})
-
-				}(i, dp, so)
 			}
 
 			return nil