Apply the emulated nullptr_t with constexpr.  This is an unusual configuration that would take advantage of this.  But it has popped up in the wild and does no harm to support it.
Apply the emulated nullptr_t with constexpr.  This is an unusual configuration that would take advantage of this.  But it has popped up in the wild and does no harm to support it.

git-svn-id: 756ef344af921d95d562d9e9f9389127a89a6314@164575 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/libcxx,llvm-mirror/libcxx,llvm-mirror/libcxx,llvm-mirror/libcxx,llvm-mirror/libcxx