Add LLVM_OVERRIDE to methods that override their base classes.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@164471 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Support/DataStream.cpp b/lib/Support/DataStream.cpp
index 94d14a5..3a38e2a 100644
--- a/lib/Support/DataStream.cpp
+++ b/lib/Support/DataStream.cpp
@@ -58,7 +58,7 @@
   virtual ~DataFileStreamer() {
     close(Fd);
   }
-  virtual size_t GetBytes(unsigned char *buf, size_t len) {
+  virtual size_t GetBytes(unsigned char *buf, size_t len) LLVM_OVERRIDE {
     NumStreamFetches++;
     return read(Fd, buf, len);
   }