Noticed that std::allocator<const T> was missing the definition for is_always_equal. Fixed this, and added a test for it.

llvm-svn: 241190
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: f43a42d53e21e5860217ede634f8eea6d25d3a18
3 files changed