[libc++] Tolerate presence of __deallocate macro

Summary:
On Windows the identifier `__deallocate` is defined as a macro by one of the Windows system headers. Previously libc++ worked around this by `#undef __deallocate` and generating a warning. However this causes the WIN32 version of `__threading_support` to always generate a warning on Windows. This is not OK.

This patch renames all usages of `__deallocate` internally as to not conflict with the macro.

Reviewers: mclow.lists, majnemer, rnk, rsmith, smeenai, compnerd

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D28426

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@291332 91177308-0d34-0410-b5e6-96231b3b80d8

include/__sso_allocator

@@ -15,8 +15,6 @@
 #include <type_traits>
 #include <new>
 
-#include <__undef___deallocate>
-
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #pragma GCC system_header
 #endif
@@ -64,7 +62,7 @@ public:
         if (__p == (pointer)&buf_)
             __allocated_ = false;
         else
-            _VSTD::__deallocate(__p);
+            _VSTD::__libcpp_deallocate(__p);
     }
     _LIBCPP_INLINE_VISIBILITY size_type max_size() const throw() {return size_type(~0) / sizeof(_Tp);}