Elide all artificial copy constructors, because
they are probably trivial. This means that we
don't confuse Clang about whether a class is
trivially copy constructible. It can figure
that out itself as long as we don't explicitly
feed it the constructors.
If the class is trivially copy-constructible,
this can change the ABI that Clang uses to call
functions that return that class (e.g., by making
the object be returned in a register), so this
is quite important for correctness.
<rdar://problem/
13457741>
llvm-svn: 178411