Record all translation units with more than one function in them (e.g., blocks).

Blocks and lambdas have their implementation functions stored in the IR for an
expression.  If we put the block/lambda into a result variable it needs to stay
around.  As a heuristic, remember any execution unit that has more than one
function in it.

<rdar://problem/22864976>

llvm-svn: 264483