os, syscall: mingw bug fixes

R=rsc
CC=golang-dev
https://golang.org/cl/815044
diff --git a/src/pkg/os/file_mingw.go b/src/pkg/os/file_mingw.go
index b9ba6a9..41bbe1e 100644
--- a/src/pkg/os/file_mingw.go
+++ b/src/pkg/os/file_mingw.go
@@ -55,7 +55,7 @@
 	if e == nil {
 		return r, nil
 	}
-	r, e = openFile(name, flag|syscall.O_CLOEXEC, perm)
+	r, e = openFile(name, flag, perm)
 	if e == nil {
 		return r, nil
 	}