C++ PATCH for c++/66999 - 'this' captured by reference

[Jason Merrill]

On 6/8/19 8:51 PM, Marek Polacek wrote:
> This patch improves a diagnostic when parsing a lambda introducer; in particular,
> we should handle '&this' better than we currently do.  clang/icc specifically
> point out that 'this' cannot be captured by reference, let's do the same.
> 
> Bootstrapped/regtested on x86_64-linux, ok for trunk?

OK.

Jason