[llvm] [XCOFF] make related SD symbols as isFunction (PR #69553)

[Chen Zheng via llvm-commits]

chenzheng1030 wrote:

Now SD/LD symbol can be separated inside XCOFF, so the new solution is totally inside the XCOFF ObjectFile.

Could you please help to review this again? @stephenpeckham @diggerlin Thanks.

https://github.com/llvm/llvm-project/pull/69553