Address a memory leak in 254760

The issue appears to have been that the copy constructor of the SmallVector was being invoked and this was somehow leading to leaked memory.  This patch avoids the symptom, but likely doesn't address the underlying problem.  I'm still investigating the root cause, but wanted to avoid the memory leak in the mean time.  Even with the underlying fix, avoiding the redundant allocation is worthwhile.

llvm-svn: 254795