Subzero: Improve class definition hygiene.

Delete zero-argument ctor where possible.

Delete default copy ctor and default assignment operator where possible (some were missed in the past).

(The above are not done to the cross tests because we aren't yet building them with C++11.)

Declare single-argument ctor as "explicit".

BUG= none
R=jfb@chromium.org

Review URL: https://codereview.chromium.org/952953002
diff --git a/src/IceELFStreamer.h b/src/IceELFStreamer.h
index ce70e86..50e4dd7 100644
--- a/src/IceELFStreamer.h
+++ b/src/IceELFStreamer.h
@@ -22,6 +22,10 @@
 // Low level writer that can that can handle ELFCLASS32/64.
 // Little endian only for now.
 class ELFStreamer {
+  ELFStreamer() = delete;
+  ELFStreamer(const ELFStreamer &) = delete;
+  ELFStreamer &operator=(const ELFStreamer &) = delete;
+
 public:
   explicit ELFStreamer(Fdstream &Out) : Out(Out) {}