Portable Python script across Python version

Make scripts more future-proof by importing most __future__ stuff.

Differential Revision: https://reviews.llvm.org/D55208

llvm-svn: 349504
diff --git a/clang/utils/perf-training/perf-helper.py b/clang/utils/perf-training/perf-helper.py
index 6337a9b..72b4b4e 100644
--- a/clang/utils/perf-training/perf-helper.py
+++ b/clang/utils/perf-training/perf-helper.py
@@ -7,7 +7,7 @@
 #
 #===------------------------------------------------------------------------===#
 
-from __future__ import print_function
+from __future__ import absolute_import, division, print_function
 
 import sys
 import os