Auto merge of #28338 - erickt:str-cmp, r=bluss
Auto merge of #28338 - erickt:str-cmp, r=bluss

llvm seems to be having some trouble optimizing the iterator-based string comparsion method into some equivalent to memcmp. This explicitly calls out to the memcmp intrinisic in order to allow llvm to generate better code. In some manual benchmarking, this memcmp-based approach is 20 times faster than the iterator approach.

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