travis: use -fno-strict-aliasing in Py2.x builds

.travis.yml

@@ -28,7 +28,7 @@ install:
 script:
   - PYTHON_DBG="python$( python -c 'import sys; print("%d.%d" % sys.version_info[:2])' )-dbg"
   - if $PYTHON_DBG -V >&2; then CFLAGS="-O0 -ggdb" $PYTHON_DBG runtests.py -vv Debugger --backends=$BACKEND; fi
-  - CFLAGS="-O2 -ggdb -Wall -Wextra" python setup.py build_ext -i
+  - CFLAGS="-O2 -ggdb -Wall -Wextra $(python -c 'import sys; print("-fno-strict-aliasing" if sys.version_info[0] == 2 else "")')" python setup.py build_ext -i
   - CFLAGS="-O0 -ggdb -Wall -Wextra" python runtests.py -vv -x Debugger --backends=$BACKEND
 
 matrix: