[llvm] [llvm-gsymutil] Suppress all error and warning messages when `--quiet` (PR #215912)

[Roy Shi via llvm-commits]

royitaqi wrote:

The failure of macOS test seems to be irrelevant to this change.
>   Failed Tests (1):
>     LLVM :: CodeGen/SPIRV/pointers/store-struct.ll

https://github.com/llvm/llvm-project/actions/runs/32067931670/job/95758724807?pr=215912#step:6:8854

https://github.com/llvm/llvm-project/pull/215912