suggest `std::move`

[llvmbot]

Bugzilla Link	19591
Version	trunk
OS	All
Reporter	LLVM Bugzilla Contributor
CC	@DougGregor,@zygoloid

Extended Description

$ cat a.cc

#include <memory>

void f(std::unique_ptr<int> i) {
  std::unique_ptr<int> j = i;
}

$ clang a.cc -std=c++11
a.cc:4:24: error: call to deleted constructor of 'std::unique_ptr<int>'
  std::unique_ptr<int> j = i;
                       ^   ~
/usr/lib/gcc/x86_64-linux-gnu/4.6/../../../../include/c++/4.6/bits/unique_ptr.h:256:7: note: 
      'unique_ptr' has been explicitly marked deleted here
      unique_ptr(const unique_ptr&) = delete;
      ^
1 error generated.

Could we detect that there is a rvalue-reference constructor and suggest that the user may have wanted to use it (or std::move)?