[Bug libstdc++/79743] New: std::experimental::optional<boolean> constructor broken in gcc 6.2

[krisk0.2017.02.27 at protonmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79743

            Bug ID: 79743
           Summary: std::experimental::optional<boolean> constructor
                    broken in gcc 6.2
           Product: gcc
           Version: lto
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: krisk0.2017.02.27 at protonmail dot com
  Target Milestone: ---

Created attachment 40841
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=40841&action=edit
all files mentioned in bug-report

Short story: std::experimental::optional<boolean> copy-constructor is broken
under GCC 6.2. 47-line .cpp proves it.

Long story as required by https://gcc.gnu.org/bugs/:
* the exact version of GCC
 sys-devel/gcc-5.3.0 --- works fine
 sys-devel/gcc-6.2.0 --- buggy
* the system type
 Gentoo on amd64 (Intel Core i5)
* the options given when GCC was configured/built
 See files 5.3.configure and 6.2.configure
* the complete command line that triggers the bug
 Install Google test --- package dev-cpp/gtest;
 g++ -std=c++14 -O2 -lgtest test.cpp && ./a.out
 Test passes under gcc 5.3 and fails under 6.2.
std::experimental::optional<boolean> constructor sets butter to false though it
should be undefined.
* the compiler output (error messages, warnings)
 None
* the preprocessed file (*.i*)
 test.5.3.ii --- works fine, test passes
 test.6.2.ii --- test fails
```
test.cpp:40: Failure
Value of: !s1.butter
  Actual: false
Expected: true
test.cpp:40: Failure
Value of: Nothing
  Actual: 1-byte object <00>
Expected: s1.butter
Which is: 2-byte object <00-01>
```