Fix a memory leak in the debug emission by simply not allocating memory.
There doesn't appear to be any reason to put this variable on the heap.
I'm suspicious of the LexicalScope above that we stuff in a map and then
delete afterward, but I'm just trying to get the valgrind bot clean.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187301 91177308-0d34-0410-b5e6-96231b3b80d8