[llvm] MIPS: fix emitDirectiveCpsetup on N32 (PR #80534)

[Fangrui Song via llvm-commits]

MaskRay wrote:



```
#if 0
```
is not recommended. Just remove the code.

Please clarify the comment. Consider the following:

In gas, .cpsetup may expand to one of two code sequences (one is related to `__gnu_local_gp`), depending on -mno-shared and -msym32.
Since Clang doesn't support -mno-shared or -msym32, .cpsetup expands to one code sequence.
The N32 condition incorrectly leads to the incorrect `__gnu_local_gp` code sequence.


https://github.com/llvm/llvm-project/pull/80534