My MacOS installs of clang/GCC are broken and cannot find libraries

In my attempt to learn C++20, I tried to get the compiler to recognize modules.

I am using Sublime Text and have set the requisite Build System (I set it to compile and then open a Terminal window to execute instead of inside Sublime Text).

Anyway, instead of reflexively just coming here to ask questions, I tried to follow various tutorials to upgrade the compiler chain so I can use modules. I went through some webpages that showed how to upgrade various things with Homebrew, etc. BUT...

Now I can't even compile simple things. Forget modules, it's not even recognizing

#include <format>#include <iostream>

somehow the search paths are broken.

Following another tutorial, I tried to locate the paths but the "find" command denies me permission to search directories even when running sudo.

So, I am at a loss now.

I don't think GCC is installed, it seems to just map to clang

gcc --version

produces:

Configured with: --prefix=/Library/Developer/CommandLineTools/usr --with-gxx-include-dir=/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/c++/4.2.1Apple clang version 12.0.5 (clang-1205.0.22.9)Target: arm64-apple-darwin20.6.0Thread model: posixInstalledDir: /Library/Developer/CommandLineTools/usr/bin

How can I fix this?