Replace -use-init-array with -use-ctors.

We have been using .init-array for most systems for quiet some time,
but tools like llc are still defaulting to .ctors because the old
option was never changed.

This patch makes llc default to .init-array and changes the option to
be -use-ctors.

Clang is not affected by this. It has its own fancier logic.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@216905 91177308-0d34-0410-b5e6-96231b3b80d8