[pair] Mark constructors as conditionally noexcept

Summary:
std::tuple marks its constructors as noexcept when the corresponding
memberwise constructors are noexcept too -- this commit improves std::pair
so that it behaves the same.

This is a re-application of r348824, which broke the build in C++03 mode
because a test was marked as supported in C++03 when it shouldn't be.

Note:
I did not add support in the explicit and non-explicit `pair(_Tuple&& __p)`
constructors because those are non-standard extensions, and supporting them
properly is tedious (we have to copy the rvalue-referenceness of the deduced
_Tuple&& onto the result of tuple_element).

<rdar://problem/29537079>

Reviewers: mclow.lists, EricWF

Subscribers: christof, llvm-commits

Differential Revision: https://reviews.llvm.org/D48669

llvm-svn: 348847

1 files changed, 3 insertions, 2 deletions

diff --git a/libcxx/test/std/utilities/utility/pairs/pairs.pair/piecewise.pass.cpp b/libcxx/test/std/utilities/utility/pairs/pairs.pair/piecewise.pass.cpp
index c738adad7d7..aa86949dd5b 100644
--- a/libcxx/test/std/utilities/utility/pairs/pairs.pair/piecewise.pass.cpp
+++ b/libcxx/test/std/utilities/utility/pairs/pairs.pair/piecewise.pass.cpp
@@ -17,9 +17,10 @@
 //     pair(piecewise_construct_t, tuple<Args1...> first_args,
 //                                 tuple<Args2...> second_args);
 
-#include <utility>
-#include <tuple>
 #include <cassert>
+#include <tuple>
+#include <utility>
+
 
 int main()
 {