[CodeGen] Eagerly emit lifetime.end markers for calls

In C, we'll wait until the end of the scope to clean up aggregate
temporaries used for returns from calls. This means in cases like:

{
  // Assuming that `Bar` is large enough to warrant indirect returns
  struct Bar b = {};
  b = foo(&b);
  b = foo(&b);
  b = foo(&b);
  b = foo(&b);
}

...We'll allocate space for 5 Bars on the stack (`b`, and 4
temporaries). This becomes painful in things like large switch
statements.

If cleaning up sooner is trivial, we should do it.

llvm-svn: 327229