name lookup on conversion function doesn't include object scope

[llvmbot]

Bugzilla Link	27807
Version	3.8
OS	Windows NT
Reporter	LLVM Bugzilla Contributor
CC	@CaseyCarter,@DougGregor

Extended Description

Clang fails to compile this example (http://stackoverflow.com/q/37310866/2069064):

struct S {
    using T = int;
    operator T() { return 42; }
};

int main() {
    S{}.operator T();
}

with:

prog.cc:7:18: error: unknown type name 'T'; did you mean 'S::T'?
    S{}.operator T();
                 ^
                 S::T
prog.cc:2:11: note: 'S::T' declared here
    using T = int;
          ^

But according to [basic.lookup.classref]/7 (updated from CWG 1111), the scope of S should be considered. gcc compiles the example.

[llvmbot]

This bug may be breaking the build of ACE/TAO 6.3.3, which introduced usage similar to this bug between 6.3.3 and 6.3.1, and now no longer compiles under clang (but still compiles under gcc).