[llvm] [TRI] Remove reserved registers in getRegPressureSetLimit (PR #118787)

[Pengcheng Wang via llvm-commits]

wangpc-pp wrote:

> Is there a compile time impact for this patch?

This should increase come compile-time, but I don't know if it is significant. The limits are cached in `RegisterClassInfo::getRegPressureSetLimit`, so it is the same for the users of this API; the limits will be calculated once in these direct users of `TargetRegisterInfo::getRegPressureSetLimit`, so it is not a performance/time-critical code path.
cc @nikic @dtcxzyw Can you help me to meassure the compile time impact?

https://github.com/llvm/llvm-project/pull/118787