Move exit condition and exit branch from exiting block into loop header and dominator...

Move exit condition and exit branch from exiting block into loop header and dominator info. This avoid execution of dead iteration. Loop is already filter in the beginning such that this change is safe.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@41394 91177308-0d34-0410-b5e6-96231b3b80d8