bad sort order for candidates

[llvmbot]

Bugzilla Link	24257
Version	unspecified
OS	All
Reporter	LLVM Bugzilla Contributor
CC	@DougGregor

Extended Description

$ cat b16776752-1.cc

struct Y {};

struct X {
  X();
  X(const X&) = delete;
  X(const X&&) = delete;
  X(Y&);
};

void test() {
  const Y y{};
  X x2(y);
}

$ clang b16776752-1.cc -std=c++14
b16776752-1.cc:12:5: error: no matching constructor for initialization of 'X'
  X x2(y);
    ^  ~
b16776752-1.cc:5:3: note: candidate constructor not viable: no known conversion
      from 'const Y' to 'const X' for 1st argument
  X(const X&) = delete;
  ^
b16776752-1.cc:6:3: note: candidate constructor not viable: no known conversion
      from 'const Y' to 'const X' for 1st argument
  X(const X&&) = delete;
  ^
b16776752-1.cc:7:3: note: candidate constructor not viable: 1st argument
      ('const Y') would lose const qualifier
  X(Y&);
  ^
b16776752-1.cc:4:3: note: candidate constructor not viable: requires 0
      arguments, but 1 was provided
  X();
  ^
1 error generated.

The two constructors are both non-viable and deleted. The X(Y&) ctor is non-viable only by a const qualifier, so it should sort ahead of the others. The deleted ctors should probably sort last.