[committed] Add gnu::unique_ptr

[Gerald Pfeifer]

On Mon, 16 Oct 2017, David Malcolm wrote:
> For reference, here's what I committed:

I'm afraid this may have broken the bootstrap with clang?

In file included from /scratch/tmp/gerald/gcc-HEAD/gcc/unique-ptr-tests.cc:23:
In file included from /scratch/tmp/gerald/gcc-HEAD/gcc/../include/unique-ptr.h:77:
In file included from /usr/include/c++/v1/memory:629:
/usr/include/c++/v1/typeinfo:199:2: error: no member named 'fancy_abort' in namespace 'std::__1'; did you mean simply 'fancy_abort'?
        _VSTD::abort();
        ^~~~~~~
/usr/include/c++/v1/__config:390:15: note: expanded from macro '_VSTD'
#define _VSTD std::_LIBCPP_NAMESPACE
              ^
/scratch/tmp/gerald/gcc-HEAD/gcc/system.h:725:13: note: 'fancy_abort' declared here
extern void fancy_abort (const char *, int, const char *)
            ^


This is FreeBSD clang version 4.0.0 (tags/RELEASE_400/final 297347) 
(based on LLVM 4.0.0), on x86_64-unknown-freebsd11.1.

Gerald