[libcxxabi] Fix the test case committed in r303175.

Free the __cxa_exception object allocated with __cxa_allocate_exception.

This is an attempt to fix this asan bot:

http://lab.llvm.org:8011/builders/libcxx-libcxxabi-x86_64-linux-ubuntu-asan/builds/560

git-svn-id: https://llvm.org/svn/llvm-project/libcxxabi/trunk@303194 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed