which parameter is to remove the nounwind readnone when use the clang to produce the .bc files

Hi,all:
I just use the clang to produce the .bc files, but by the .ll files converted by the .bc files.
I found that there some keywords " nounwind readnone" in the .ll files,
Is there some parameters that I can use to remove them when use the clang?

Thanks,
yaoxiao

Try generate .bc with -O0