R600/SI: Fix verifier error caused by SIAnnotateControlFlow

This pass will always try to insert llvm.SI.ifbreak intrinsics
in the same block that its conditional value is computed in.  This is
a problem when conditions for breaks or continue are computed outside
of the loop, because the llvm.SI.ifbreak intrinsic ends up being inserted
outside of the loop.

This patch fixes this problem by inserting the llvm.SI.ifbreak
intrinsics in the loop header when the condition is computed outside
the loop.

llvm-svn: 234891