Add another hint for fixing check-polly errors to get_started.html

Reversed the order in which LD_LIBRARY_PATH is defined in order to make sure the
${CLOOG_INSTALL} prefix is found first.

Contributed-by: Christian Bielert <cib123@googlemail.com>

git-svn-id: https://llvm.org/svn/llvm-project/polly/trunk@205556 91177308-0d34-0410-b5e6-96231b3b80d8