Based on post-commit feedback over IRC with dblaikie, ideally, we should have a Small...

Based on post-commit feedback over IRC with dblaikie, ideally, we should have a SmallVector constructor that accepts anything which can supply a range via ADL begin()/end() calls so that we can construct the SmallVector directly from anything range-like.

Since that doesn't exist right now, use a local variable instead of calling getAssocExprs() twice; NFC.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@280520 91177308-0d34-0410-b5e6-96231b3b80d8