Debug Info: LiveDebugVarible can remove DBG_VALUEs, make sure we emit them back.

Debug Info: LiveDebugVarible can remove DBG_VALUEs, make sure we emit them back.

RegisterCoalescer used to depend on LiveDebugVariable. LDV removes DBG_VALUEs
without emitting them at the end.

We fix this by removing LDV from RegisterCoalescer. Also add an assertion to
make sure we call emitDebugValues if DBG_VALUEs are removed at
runOnMachineFunction.

rdar://problem/13183203
Reviewed by Andy & Jakob

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@175023 91177308-0d34-0410-b5e6-96231b3b80d8