Replacing push_back() with emplace_back() eliminates the calls to the
copy constructor, but I still had to provide explicit copy constructors
because of the call to vector::reserve(), which tries to instantiate them
even though they'll never actually be called when reserve() is called
on an empty vector.
gold/
	* incremental.cc (Sized_incremental_binary::setup_readers): Use
	emplace_back for GCC 5 and later.
	* incremental.h (Incremental_binary::Input_reader): Provide copy
	constructor.
	(Sized_incremental_binary::Sized_input_reader): Likewise.
+2018-06-22  Cary Coutant  <ccoutant@gmail.com>
+
+       * incremental.cc (Sized_incremental_binary::setup_readers): Use
+       emplace_back for GCC 5 and later.
+       * incremental.h (Incremental_binary::Input_reader): Provide copy
+       constructor.
+       (Sized_incremental_binary::Sized_input_reader): Likewise.
+
 2018-06-22  Cary Coutant  <ccoutant@gmail.com>
 
        PR gold/22914
 
   for (unsigned int i = 0; i < count; i++)
     {
       Input_entry_reader input_file = inputs.input_file(i);
+#if defined(__GNUC__) && __GNUC__ < 5
       this->input_entry_readers_.push_back(Sized_input_reader(input_file));
+#else
+      this->input_entry_readers_.emplace_back(input_file);
+#endif
       switch (input_file.type())
        {
        case INCREMENTAL_INPUT_OBJECT:
 
     Input_reader()
     { }
 
+    Input_reader(const Input_reader&)
+    { }
+
     virtual
     ~Input_reader()
     { }
       : Input_reader(), reader_(r)
     { }
 
+    Sized_input_reader(const Sized_input_reader& r)
+      : Input_reader(), reader_(r.reader_)
+    { }
+
     virtual
     ~Sized_input_reader()
     { }