[Bug c++/64816] gcc claims that constructor is private when it should be accessible

[thakis at chromium dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64816

--- Comment #1 from thakis at chromium dot org ---
(Here's a patch with a libc++-side workaround: http://reviews.llvm.org/D7201
But it'd be good to fix this in the compiler too, of course.)