llvm-dwp: Fix the build by moving DWPStringPool into the llvm namespace

llvm-svn: 270453
diff --git a/llvm/tools/llvm-dwp/DWPStringPool.h b/llvm/tools/llvm-dwp/DWPStringPool.h
index 8923e4c..7d41176 100644
--- a/llvm/tools/llvm-dwp/DWPStringPool.h
+++ b/llvm/tools/llvm-dwp/DWPStringPool.h
@@ -6,6 +6,7 @@
 #include "llvm/MC/MCStreamer.h"
 #include <cassert>
 
+namespace llvm {
 class DWPStringPool {
 
   struct CStrDenseMapInfo {
@@ -50,5 +51,6 @@
     return Pair.first->second;
   }
 };
+}
 
 #endif