not instantiate exception specifications of functions if they were only used in
unevaluated contexts (other than 'noexcept' expressions).

In C++17 onwards, this becomes essential since the exception specification is
now part of the function's type.

Note that this means that constructs like the following no longer work:

  struct A {
    static T f() noexcept(...);
    decltype(f()) *p;
  };

... because the decltype expression now needs the exception specification of
'f', which has not yet been parsed.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@284549 91177308-0d34-0410-b5e6-96231b3b80d8