Fix for D25504 - segfault because of double free()-ing in shutdown code.

Paul Osmialowski pointed out a double free bug in shutdown code.  This patch
Moves the freeing of the implicit task to above the freeing of all fast memory
to prevent the double-free issue.

Differential Revision: https://reviews.llvm.org/D26860


git-svn-id: https://llvm.org/svn/llvm-project/openmp/trunk@287551 91177308-0d34-0410-b5e6-96231b3b80d8