Homebrew/homebrew — pull request #33080 by johannkoenig (2014-10-10 18:56:10+00:00)
Title: Enable runtime cpu detection

Runtime cpu detect allows the compiler to build the library with the highest possible optimizations and select what is available at run time. However, disabling it does not verify that the current processor is able to run the code being built. Upstream now includes AVX2 code which, although it will build with recent versions of XCode, will not run on many devices and will crash.