Sorry, but the /usr model for compiling is out of date / flawed. It isn't about "me" it is about "you" the target for running the executable. For many years, m

Sorry, but the /usr model for compiling is out of date / flawed. It isn't about "me" it is about "you" the target for running the executable. For many years, macOS has supported being a cross compilation environment for multiple platforms and multiple OS releases. This means that include files and libraries for the target OS and platform are not stored at the "host filesystem" paths that were used in the 1960's, 1970's and 1980's... (an embarrassingly long list). Include files and references to libraries are available in the SDKs. One should use the SDK path as a prefix for the include and library paths - something that most GNU tools, and other open source projects have supported for a very long time, but sadly a little inconsistently. There are runtime tools and recipes that can be used to get these paths, including for "myself". All compilation on macOS should be considered as cross compilation -- because macOS simultaneously supports multiple architectures and OS versions. This really is a good abstracted model for all compilation. This has benefits! Install time and disk space usage are reduced for most customers and developers. Developers on x86_64 do not need the aarch64 content in /System, /usr to compile. Install the SDKs for the targets you wish to compile for.