Implement "optimization" for lambda-to-block conversion which inlines the generated block literal for lambdas which are immediately converted to block pointer type.  This simplifies the AST, avoids an unnecessary copy of the lambda and makes it much easier to avoid copying the result onto the heap.

Note that this transformation has a substantial semantic effect outside of ARC: it gives the converted lambda lifetime semantics similar to a block literal.  With ARC, the effect is much less obvious because the lifetime of blocks is already managed.

llvm-svn: 151797