[llvm] [InstCombine] simplify `icmp pred x, ~x` (PR #73990)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-clang-x86_64-sie-win` running on `sie-win-worker` while building `llvm` at step 7 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/46/builds/11693

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 7 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'LLVM :: Transforms/InstCombine/icmp-of-xor-x.ll' FAILED ********************
Exit Code: 1

Command Output (stdout):
--
# RUN: at line 2
z:\b\llvm-clang-x86_64-sie-win\build\bin\opt.exe < Z:\b\llvm-clang-x86_64-sie-win\llvm-project\llvm\test\Transforms\InstCombine\icmp-of-xor-x.ll -passes=instcombine -S | z:\b\llvm-clang-x86_64-sie-win\build\bin\filecheck.exe Z:\b\llvm-clang-x86_64-sie-win\llvm-project\llvm\test\Transforms\InstCombine\icmp-of-xor-x.ll
# executed command: 'z:\b\llvm-clang-x86_64-sie-win\build\bin\opt.exe' -passes=instcombine -S
# executed command: 'z:\b\llvm-clang-x86_64-sie-win\build\bin\filecheck.exe' 'Z:\b\llvm-clang-x86_64-sie-win\llvm-project\llvm\test\Transforms\InstCombine\icmp-of-xor-x.ll'
# .---command stderr------------
# | Z:\b\llvm-clang-x86_64-sie-win\llvm-project\llvm\test\Transforms\InstCombine\icmp-of-xor-x.ll:127:15: error: CHECK-NEXT: expected string not found in input
# | ; CHECK-NEXT: [[CMP:%.*]] = icmp sgt <2 x i8> [[X:%.*]], <i8 -1, i8 -1>
# |               ^
# | <stdin>:66:30: note: scanning from here
# | define <2 x i1> @src_sgt_vec(<2 x i8> %x) {
# |                              ^
# | <stdin>:67:2: note: possible intended match here
# |  %cmp = icmp sgt <2 x i8> %x, splat (i8 -1)
# |  ^
# | Z:\b\llvm-clang-x86_64-sie-win\llvm-project\llvm\test\Transforms\InstCombine\icmp-of-xor-x.ll:148:15: error: CHECK-NEXT: expected string not found in input
# | ; CHECK-NEXT: [[CMP:%.*]] = icmp sgt <2 x i8> [[X:%.*]], <i8 -1, i8 -1>
# |               ^
# | <stdin>:76:30: note: scanning from here
# | define <2 x i1> @src_sge_vec(<2 x i8> %x) {
# |                              ^
# | <stdin>:77:2: note: possible intended match here
# |  %cmp = icmp sgt <2 x i8> %x, splat (i8 -1)
# |  ^
# | Z:\b\llvm-clang-x86_64-sie-win\llvm-project\llvm\test\Transforms\InstCombine\icmp-of-xor-x.ll:169:15: error: CHECK-NEXT: expected string not found in input
# | ; CHECK-NEXT: [[CMP:%.*]] = icmp sgt <2 x i8> [[X:%.*]], <i8 -1, i8 -1>
# |               ^
# | <stdin>:86:30: note: scanning from here
# | define <2 x i1> @src_ult_vec(<2 x i8> %x) {
# |                              ^
# | <stdin>:87:2: note: possible intended match here
# |  %cmp = icmp sgt <2 x i8> %x, splat (i8 -1)
# |  ^
# | Z:\b\llvm-clang-x86_64-sie-win\llvm-project\llvm\test\Transforms\InstCombine\icmp-of-xor-x.ll:190:15: error: CHECK-NEXT: expected string not found in input
# | ; CHECK-NEXT: [[CMP:%.*]] = icmp sgt <2 x i8> [[X:%.*]], <i8 -1, i8 -1>
# |               ^
# | <stdin>:96:30: note: scanning from here
# | define <2 x i1> @src_ule_vec(<2 x i8> %x) {
# |                              ^
# | <stdin>:97:2: note: possible intended match here
# |  %cmp = icmp sgt <2 x i8> %x, splat (i8 -1)
# |  ^
# | Z:\b\llvm-clang-x86_64-sie-win\llvm-project\llvm\test\Transforms\InstCombine\icmp-of-xor-x.ll:200:15: error: CHECK-NEXT: expected string not found in input
# | ; CHECK-NEXT: [[CMP:%.*]] = icmp sgt <2 x i8> [[X:%.*]], <i8 -1, i8 -1>
# |               ^
# | <stdin>:101:34: note: scanning from here
...

```

</details>

https://github.com/llvm/llvm-project/pull/73990