Move stringpiece.h and stringprintf.h to base/.

Change-Id: I7f71b4a12f99c5f81771146c66629ae5a947b229
diff --git a/src/compiler_llvm/utils_llvm.h b/src/compiler_llvm/utils_llvm.h
index 5ad68d0..cec21dc 100644
--- a/src/compiler_llvm/utils_llvm.h
+++ b/src/compiler_llvm/utils_llvm.h
@@ -17,7 +17,7 @@
 #ifndef ART_SRC_UTILS_LLVM_H_
 #define ART_SRC_UTILS_LLVM_H_
 
-#include "stringprintf.h"
+#include "base/stringprintf.h"
 
 #include <llvm/Analysis/Verifier.h>