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

llvm-svn: 336159
diff --git a/llvm/lib/Demangle/ItaniumDemangle.cpp b/llvm/lib/Demangle/ItaniumDemangle.cpp
index c7bba85..b7e2e27 100644
--- a/llvm/lib/Demangle/ItaniumDemangle.cpp
+++ b/llvm/lib/Demangle/ItaniumDemangle.cpp
@@ -1951,7 +1951,7 @@
   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() {