python compat - no explicit reference to python version

[michaelplatings]

LGTM

llvm/trunk/docs/TestSuiteGuide.md

1. The lit test runner is required to run the tests. You can either use one
    lit 0.8.0dev
    ```
 
    An alternative is installing it as a python package in a python virtual
    environment:
 
    ```bash
    % mkdir venv
-   % virtualenv -p python2.7 venv
+   % virtualenv venv
    % . venv/bin/activate
    % pip install svn+http://llvm.org/svn/llvm-project/llvm/trunk/utils/lit
    % lit --version
    lit 0.8.0dev
    ```
 
 2. Check out the `test-suite` module with:
 

llvm/trunk/tools/opt-viewer/opt-diff.py

-#!/usr/bin/env python2.7
+#!/usr/bin/env python
 
 from __future__ import print_function
 
 desc = '''Generate the difference of two YAML files into a new YAML file (works on
 pair of directories too).  A new attribute 'Added' is set to True or False
 depending whether the entry is added or removed from the first input to the
 next.
 

llvm/trunk/tools/opt-viewer/opt-stats.py

-#!/usr/bin/env python2.7
+#!/usr/bin/env python
 
 from __future__ import print_function
 
 desc = '''Generate statistics about optimization records from the YAML files
 generated with -fsave-optimization-record and -fdiagnostics-show-hotness.
 
 The tools requires PyYAML and Pygments Python packages.'''
 

llvm/trunk/tools/opt-viewer/opt-viewer.py

-#!/usr/bin/env python2.7
+#!/usr/bin/env python
 
 from __future__ import print_function
 
 import argparse
 import cgi
 import codecs
 import errno
 import functools

llvm/trunk/tools/opt-viewer/optrecord.py

-#!/usr/bin/env python2.7
+#!/usr/bin/env python
 
 from __future__ import print_function
 
 import yaml
 # Try to use the C parser.
 try:
     from yaml import CLoader as Loader
 except ImportError:

llvm/trunk/utils/update_analyze_test_checks.py

-#!/usr/bin/env python2.7
+#!/usr/bin/env python
 
 """A script to generate FileCheck statements for 'opt' analysis tests.
 
 This script is a utility to update LLVM opt analysis test cases with new
 FileCheck patterns. It can either update all of the tests in the file or
 a single test function.
 
 Example usage:

llvm/trunk/utils/update_llc_test_checks.py

-#!/usr/bin/env python2.7
+#!/usr/bin/env python
 
 """A test case update script.
 
 This script is a utility to update LLVM 'llc' based test cases with new
 FileCheck patterns. It can either update all of the tests in the file or
 a single test function.
 """
 

llvm/trunk/utils/update_mca_test_checks.py

-#!/usr/bin/env python2.7
+#!/usr/bin/env python
 
 """A test case update script.
 
 This script is a utility to update LLVM 'llvm-mca' based test cases with new
 FileCheck patterns.
 """
 
 import argparse

llvm/trunk/utils/update_test_checks.py

-#!/usr/bin/env python2.7
+#!/usr/bin/env python
 
 """A script to generate FileCheck statements for 'opt' regression tests.
 
 This script is a utility to update LLVM opt test cases with new
 FileCheck patterns. It can either update all of the tests in the file or
 a single test function.
 
 Example usage: