[llvm] [AMDGPU] Do not use original PHIs in coercion chains (PR #98063)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `arc-builder` running on `arc-worker` while building `llvm` at step 5 "build-unified-tree".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/3/builds/1341

Here is the relevant piece of the build log for the reference:
```
Step 5 (build-unified-tree) failure: build (failure)
...
28.606 [2/11/104] Linking CXX executable bin/llvm-exegesis
28.613 [2/10/105] Linking CXX executable bin/llvm-isel-fuzzer
29.375 [2/9/106] Linking CXX executable bin/llvm-split
30.612 [2/8/107] Linking CXX executable bin/llvm-opt-fuzzer
31.225 [2/7/108] Linking CXX executable bin/llvm-reduce
31.788 [2/6/109] Linking CXX executable bin/llvm-lto2
32.183 [2/5/110] Linking CXX executable bin/clang-19
32.184 [1/5/111] Linking CXX executable bin/opt
32.198 [1/4/112] Creating executable symlink bin/clang
32.429 [1/3/113] Linking CXX executable bin/clang-repl
command timed out: 1200 seconds without output running [b'ninja', b'-j', b'16'], attempting to kill
process killed by signal 9
program finished with exit code -1
elapsedTime=1275.530542

```

https://github.com/llvm/llvm-project/pull/98063