Fix avr sample.

- Incompatible ISL/CLooG were requested by config after newer releases
of both were brought in.
- Consistency with other samples: save tarballs (which will avoid
  downloading them each time from Travis), extra logging.

samples/avr/crosstool.config

@@ -1,5 +1,8 @@
+CT_LOCAL_TARBALLS_DIR="${HOME}/src"
+CT_SAVE_TARBALLS=y
+CT_LOG_EXTRA=y
 CT_ARCH_avr=y
 CT_CC_GCC_V_4_9_2=y
 CT_CC_LANG_CXX=y
 CT_DEBUG_gdb=y
-CT_ISL_V_0_12_2=y
+CT_CLOOG_V_0_18_1=y