[llvm] [Verifier] Reject va_start in non-variadic function (PR #88809)

[Ivan Butygin via llvm-commits]

Hardcode84 wrote:

This change broke MLIR tests (PR buildkite failed as well), they are probably needeed to be updated
```
******************** TEST 'MLIR :: Target/LLVMIR/Import/intrinsic.ll' FAILED ********************
Exit Code: 2

Command Output (stdout):
--
# RUN: at line 1
/var/lib/buildkite-agent/builds/linux-56-59b8f5d88-6mhbj-1/llvm-project/github-pull-requests/build/bin/mlir-translate -import-llvm /var/lib/buildkite-agent/builds/linux-56-59b8f5d88-6mhbj-1/llvm-project/github-pull-requests/mlir/test/Target/LLVMIR/Import/intrinsic.ll | /var/lib/buildkite-agent/builds/linux-56-59b8f5d88-6mhbj-1/llvm-project/github-pull-requests/build/bin/FileCheck /var/lib/buildkite-agent/builds/linux-56-59b8f5d88-6mhbj-1/llvm-project/github-pull-requests/mlir/test/Target/LLVMIR/Import/intrinsic.ll
# executed command: /var/lib/buildkite-agent/builds/linux-56-59b8f5d88-6mhbj-1/llvm-project/github-pull-requests/build/bin/mlir-translate -import-llvm /var/lib/buildkite-agent/builds/linux-56-59b8f5d88-6mhbj-1/llvm-project/github-pull-requests/mlir/test/Target/LLVMIR/Import/intrinsic.ll
# .---command stderr------------
# | va_start called in a non-varargs function
# `-----------------------------
# error: command failed with exit status: 1
# executed command: /var/lib/buildkite-agent/builds/linux-56-59b8f5d88-6mhbj-1/llvm-project/github-pull-requests/build/bin/FileCheck /var/lib/buildkite-agent/builds/linux-56-59b8f5d88-6mhbj-1/llvm-project/github-pull-requests/mlir/test/Target/LLVMIR/Import/intrinsic.ll
# .---command stderr------------
# | FileCheck error: '<stdin>' is empty.
# | FileCheck command line:  /var/lib/buildkite-agent/builds/linux-56-59b8f5d88-6mhbj-1/llvm-project/github-pull-requests/build/bin/FileCheck /var/lib/buildkite-agent/builds/linux-56-59b8f5d88-6mhbj-1/llvm-project/github-pull-requests/mlir/test/Target/LLVMIR/Import/intrinsic.ll
# `-----------------------------
# error: command failed with exit status: 2
```

https://github.com/llvm/llvm-project/pull/88809