Auto merge of #38296 - dylanmckay:llvm-4.0-errortype, r=alexcrichton
Auto merge of #38296 - dylanmckay:llvm-4.0-errortype, r=alexcrichton

[LLVM 4.0] Explicitly call constructor of 'llvm::Error'

The implicit constructor has been deleted. We should use
Error::success() instead.

The constructor in the LLVM headers mentions that "success" should be
used instead of the deleted constructor for clarity.

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