Fix build on windows.

llvm-svn: 210873
diff --git a/llvm/lib/Support/MemoryBuffer.cpp b/llvm/lib/Support/MemoryBuffer.cpp
index a8f3385..8ff4e7c 100644
--- a/llvm/lib/Support/MemoryBuffer.cpp
+++ b/llvm/lib/Support/MemoryBuffer.cpp
@@ -373,7 +373,7 @@
   size_t BytesLeft = MapSize;
 #ifndef HAVE_PREAD
   if (lseek(FD, Offset, SEEK_SET) == -1)
-    return error_code(errno, std::generic_category());
+    return std::error_code(errno, std::generic_category());
 #endif
 
   while (BytesLeft) {