[llvm] [DFAJumpThreading] Enable DFAJumpThread by default. (PR #157646)

[Hongyu Chen via llvm-commits]

XChy wrote:

The current implementation is conservative and optimizes only one switch. After numerous fixes, this pass has become more stable and safe. For me, it's acceptable to enable this pass now if there is no severe compile-time regression. And enabling it will uncover more hidden problems.
My main concern is that compile-time may increase massively if we optimize multiple switches in the future, though we don't allow it currently.
Anyway, I am not against enabling DFAJumpThreading by default.

https://github.com/llvm/llvm-project/pull/157646