Rollup merge of #31741 - alexcrichton:fix-ios, r=nikomatsakis
Rollup merge of #31741 - alexcrichton:fix-ios, r=nikomatsakis

Similar to OSX, these symbols are prefixed by default.

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