Some buildbots were choking on std::max_align_t, try using the global alias.

git-svn-id: https://llvm.org/svn/llvm-project/libcxxabi/trunk@336159 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/src/cxa_demangle.cpp b/src/cxa_demangle.cpp
index 1cdc29b..401f394 100644
--- a/src/cxa_demangle.cpp
+++ b/src/cxa_demangle.cpp
@@ -1891,7 +1891,7 @@
   static constexpr size_t AllocSize = 4096;
   static constexpr size_t UsableAllocSize = AllocSize - sizeof(BlockMeta);
 
-  alignas(std::max_align_t) char InitialBuffer[AllocSize];
+  alignas(max_align_t) char InitialBuffer[AllocSize];
   BlockMeta* BlockList = nullptr;
 
   void grow() {