[libc++][nfc] Only test if pair is_assignable after C++03.
authorzoecarver <z.zoelec2@gmail.com>
Fri, 19 Feb 2021 23:12:19 +0000 (15:12 -0800)
committerzoecarver <z.zoelec2@gmail.com>
Fri, 19 Feb 2021 23:14:44 +0000 (15:14 -0800)
commit6c75a84ce76789d065b29e5966254e4943d7dba8
tree361f516f59a5f9f8c326215a7ed653e145e5d5a6
parent99fc4a65847a7020ae328e42a67e80cc29c1e762
[libc++][nfc] Only test if pair is_assignable after C++03.

In C++03 libc++ uses a different set of constructors which aren't
constrained, so these tests won't work. This should fix the bots.

Refs: 82c4701.
libcxx/test/std/utilities/utility/pairs/pairs.pair/assign_const_pair_U_V.pass.cpp