[llvm] [InlineCost] Consider the default branch when calculating cost (PR #77856)

[Yingwei Zheng via llvm-commits]

dtcxzyw wrote:

Emm, looks like a lot of callees cannot be inlined after this patch.
I'd like to decrease the inline cost of `switch w/ unreachable default branch` cases, instead of increasing the cost of other common cases.


https://github.com/llvm/llvm-project/pull/77856