Omit extracting a loop if one of the exits is a landing pad.

Omit extracting a loop if one of the exits is a landing pad.

The landing pad must accompany the invoke when it's extracted. However, if it
does, then the loop isn't properly extracted. I.e., the resulting extraction has
a loop in it. The extracted function is then extracted, etc. resulting in an
infinite loop.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@140193 91177308-0d34-0410-b5e6-96231b3b80d8