[llvm] [IR] Add `samesign` flag to icmp instruction (PR #111419)

[via llvm-commits]

elhewaty wrote:

@nikic @dtcxzyw, these are failed tests, any hints why?
```
Failed Tests (16):
  LLVM :: Assembler/auto_upgrade_nvvm_intrinsics.ll
  LLVM :: Assembler/flags.ll
  LLVM :: Bindings/llvm-c/echo.ll
  LLVM :: Bitcode/compatibility-3.6.ll
  LLVM :: Bitcode/compatibility-3.7.ll
  LLVM :: Bitcode/compatibility-3.8.ll
  LLVM :: Bitcode/compatibility-3.9.ll
  LLVM :: Bitcode/compatibility-4.0.ll
  LLVM :: Bitcode/compatibility-5.0.ll
  LLVM :: Bitcode/compatibility-6.0.ll
  LLVM :: Bitcode/compatibility.ll
  LLVM :: Bitcode/flags.ll
  LLVM :: Bitcode/miscInstructions.3.2.ll
  LLVM :: Feature/basictest.ll
  LLVM :: Feature/recursivetype.ll
  LLVM :: Integer/basictest_bt.ll
```

and here is one failure message that I don't understand:
```
FAIL: LLVM :: Assembler/flags.ll (1 of 53995)
******************** TEST 'LLVM :: Assembler/flags.ll' FAILED ********************
Exit Code: 2

Command Output (stderr):
--
RUN: at line 1: myLLVM/build/bin/llvm-as < myLLVM/llvm-project/llvm/test/Assembler/flags.ll | myLLVM/build/bin/llvm-dis | myLLVM/build/bin/FileCheck myLLVM/llvm-project/llvm/test/Assembler/flags.ll
+ myLLVM/build/bin/llvm-as
+ myLLVM/build/bin/llvm-dis
+ myLLVM/build/bin/FileCheck myLLVM/llvm-project/llvm/test/Assembler/flags.ll
myLLVM/build/bin/llvm-dis: error: Invalid record (Producer: 'LLVM20.0.0git' Reader: 'LLVM 20.0.0git')
FileCheck error: '<stdin>' is empty.
FileCheck command line:  myLLVM/build/bin/FileCheck myLLVM/llvm-project/llvm/test/Assembler/flags.ll

--
```



https://github.com/llvm/llvm-project/pull/111419