Store the global variable that's created so that it's reclaimed afterwards.

This plugs a memory leak in ARM's FastISel by storing the GV in Module so that
it's reclaimed.
PR17978

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198160 91177308-0d34-0410-b5e6-96231b3b80d8