was caused by upstream libc++ commit r194536, which aimed to make the
headers more standards-compliant, by making std::pair's copy constructor
trivial. Unfortunately, this could cause certain C++ applications using
shared libraries built against the previous version of libc++ to crash.
Fix the ABI incompatibility by making std::pair's copy constructor
non-trivial again.
Please note: Any C++ applications or shared libraries built with libc++
between r261283 and this revision should be recompiled.
Reported by: stefanf
MFC after: 3 weeks
X-MFC-With: r261283
eed07a2ea1