[PATCH] Improve error reporting for SFINAE

[Richard Smith]

As noted on PR13309, this is not acceptable as-is -- note that the sample diagnostic:

  smurf.cpp:6:3: error: no matching function for call to 'f'
    f(3);
    ^
  smurf.cpp:3:41: note: candidate template ignored: substitution failure [with T = int]: no matching function for call to 'h'
  template<class T> auto g(T x)->decltype(h(x)){return h(x);}

... gives the user no idea of how we got from a call to `f` into a call to `g`. If we produced a stack of 'in instantiation of' notes, this would be fine (note that's exactly what my patch in comment#1/comment#2 of that bug does).


REPOSITORY
  rL LLVM

http://reviews.llvm.org/D8309

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