Recently, Apple released an update that broke every C-based Python package, and probably more (the “-mno-fused-madd” compilation error). See here for more information.

To fix, add these to your environment:

export CFLAGS=-Qunused-arguments
export CPPFLAGS=-Qunused-arguments

Then, add this to your sudoers file (via visudo), which will allow sudo to have access to those variables:

Defaults        env_keep += "CFLAGS CPPFLAGS"