[IRGen] Emit lifetime markers for temporary struct allocas

When passing arguments using temporary allocas, we need to add the
appropriate lifetime markers so that the stack coloring passes can
re-use the stack space.

This patch keeps track of all the lifetime.start calls emited before the
codegened call, and adds the corresponding lifetime.end calls after the
call.

Differential Revision: https://reviews.llvm.org/D68611

llvm-svn: 374126