Compiling some C++ code simple module using clang/gcc

I was trying for sake of practice to compile a small module using clang (which is the compiler I have in hand at the moment).

My module code is:

//basic_math.cpp
export module basic.math; //Notice module name is not the same as filename

int mysum(int x, int y) {  // no export keyword implies module linkage
  return x + y;
}

export int add(int x, int y) { return mysum(x, y); }

And my main

import basic.math;
#include <iostream>

int main()
{
    auto res = add(3, 5);
    std::cout << res << '\n';
    return 0;
}

I've tried several options, mainly from chatgpt as I wanted to get it going quickly.

clang++ -std=c++20 -fmodules -fcxx-modules -nostdinc++ -isystem /opt/homebrew/opt/llvm/include/c++/v1 -x c++-module -c basic_math.cpp -o basic_math.pcm && clang++ -std=c++20 -fmodules -fcxx-modules -nostdinc++ -isystem /opt/homebrew/opt/llvm/include/c++/v1 -fmodule-file=basic_math.pcm -c main.cpp -o main.o && clang++ -std=c++20 -fmodules -fcxx-modules -nostdinc++ -isystem /opt/homebrew/opt/llvm/include/c++/v1 main.o -o main

The error I get is:

fatal error: file 'basic_math.pcm' is not a valid precompiled module file: file too small to contain AST file magic
1 error generated.

My clang version is

Homebrew clang version 20.1.4
Target: arm64-apple-darwin24.4.0
Thread model: posix
InstalledDir: /opt/homebrew/Cellar/llvm/20.1.4_1/bin
Configuration file: /opt/homebrew/etc/clang/arm64-apple-darwin24.cfg

which I thought supported modules. I've also tried gcc with several commands with no success.

I am starting to wonder if modules, despite being part of C++20, are actually supported properly by any compiler. So far I've tried gcc 14 and clang 20.

Can anyone tell me if:

1. Modules are actually supported
2. What is the right way to compile the code I've shown?