Bug 1684914: stop passing `-flto=thin` to gcc since it doesn't actually work...
Bug 1684914: stop passing `-flto=thin` to gcc since it doesn't actually work r=glandium,mhentges a=RyanVM Passing `-flto=thin` worked previously but the value passed was just ignored and full lto was performed. On newer versions of gcc passing an unknown value causes failure. So this commit checks if `-flto=thin` is passed and fails with an error message if so, else full lto is enabled if any other value is passed. Differential Revision: https://phabricator.services.mozilla.com/D100953