[Bug libstdc++/80762] is_constructible<filesystem::path, void> gives hard error with clang

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80762

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Author: redi
Date: Thu Jan 10 16:06:49 2019
New Revision: 267815

URL: https://gcc.gnu.org/viewcvs?rev=267815&root=gcc&view=rev
Log:
PR libstdc++/80762 avoid ambiguous __constructible_from<void, void>

Ensure we don't try to instantiate __is_constructible_from<void, void>,
because there are two partial specializations that are equally good
matches.

Backport from mainline
2018-12-12  Jonathan Wakely  <jwakely@redhat.com>

        PR libstdc++/80762
        * include/bits/fs_path.h (path::_Path): Use remove_cv_t and is_void.
        * include/experimental/bits/fs_path.h (path::_Path): Likewise.
        * testsuite/27_io/filesystem/path/construct/80762.cc: New test.
        * testsuite/experimental/filesystem/path/construct/80762.cc: New test.

Added:
   
branches/gcc-8-branch/libstdc++-v3/testsuite/27_io/filesystem/path/construct/80762.cc
   
branches/gcc-8-branch/libstdc++-v3/testsuite/experimental/filesystem/path/construct/80762.cc
Modified:
    branches/gcc-8-branch/libstdc++-v3/ChangeLog
    branches/gcc-8-branch/libstdc++-v3/include/bits/fs_path.h
    branches/gcc-8-branch/libstdc++-v3/include/experimental/bits/fs_path.h