As far as I can tell this configuration flag affects only the gmp and givaro packages. There are two problems that I have run into with it.

1. It is misnamed. What Apple means by a "fat binary" is a single mach-O file containing multiple binaries for different CPU architectures. That is not what this flag produces. The name was probably derived from the gmp configure flag --enable-fat, which is used when SAGE_FAT_BINARY is yes. That gmp flag causes gmp to include assembly language modules for all possible Intel variants, and to add code that selects which of those modules to use at run time.

2. It does the wrong thing for givaro. Currently in the givaro package it disables all intel extensions (the opposite of making it "fat") by setting the configure flags: -mno-sse, -mno-sse2, -mno-avx, -mno-avx2, and -mno-bmi2. But sse and sse2 should not be disabled, at least not on macOS. All of the relevent Intel chips used by Apple support those instruction sets. (And conda does not disable them, by the way.) Sage will not build on Apple systems with older Intel chips for other reasons.

A better name might be ENABLE_INTEL_COMPATIBILITY.

CC: @kliem @jhpalmieri

Component: build: configure

Issue created by migration from https://trac.sagemath.org/ticket/32363