rustbuild: Fix a distribution bug with rustdoc
rustbuild: Fix a distribution bug with rustdoc

Apparently `File::create` was called when there was an existing hard link or the
like, causing an existing file to get accidentally truncated!

Closes #44487

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