re PR libstdc++/79141 (std::pair<int,int> p = {}; fails to compile due to ambiguous...

re PR libstdc++/79141 (std::pair<int,int> p = {}; fails to compile due to ambiguous overload)

PR libstdc++/79141
* include/bits/stl_pair.h (__nonesuch_no_braces): New.
(operator=(typename conditional<
__and_<is_copy_assignable<_T1>,
is_copy_assignable<_T2>>::value,
const pair&, const __nonesuch&>::type)): Change __nonesuch
to __nonesuch_no_braces.
(operator=(typename conditional<
__not_<__and_<is_copy_assignable<_T1>,
is_copy_assignable<_T2>>>::value,
const pair&, const __nonesuch&>::type)): Likewise.
(operator=(typename conditional<
__and_<is_move_assignable<_T1>,
is_move_assignable<_T2>>::value,
pair&&, __nonesuch&&>::type)): Likewise.
* testsuite/20_util/pair/79141.cc: New.

From-SVN: r246653