From r229162:
Visual Studio's SAL extension uses a macro named __deallocate. This
macro is used pervasively
Using -Werror when building for Windows can force the use of -Wno-#warnings
specifically because of this __deallocate #warning. Instead of forcing
builds to disable all #warnings, this option allows libc++ to be built
without this particular warning, while leaving other #warnings enabled.
Patch by Dave Lee!
git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@275172 91177308-0d34-0410-b5e6-96231b3b80d8
