Always forward 'resume' instructions to the outter landing pad.

How did this ever work?

Basically, if you have a function that's inlined into the caller, it may not
have any 'call' instructions, but any 'resume' instructions it may have should
still be forwarded to the outer (caller's) landing pad. This requires that all
of the 'landingpad' instructions in the callee have their clauses merged with
the caller's outer 'landingpad' instruction (hence the bit of ugly code in the
`forwardResume' method).

Testcase in a follow commit to the test-suite repository.

<rdar://problem/13360379> & PR15555


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@177680 91177308-0d34-0410-b5e6-96231b3b80d8