Allow cleaning llvm build dir to fail
Allow cleaning llvm build dir to fail

It may not exist, so we don't want to spuriously generate an error.

GBGamer/rust,GBGamer/rust,graydon/rust,graydon/rust,GBGamer/rust,GBGamer/rust,aidancully/rust,GBGamer/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,GBGamer/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,GBGamer/rust,graydon/rust,GBGamer/rust