Is clang-11's invocation of headers via -fcoroutines flag?

I’m trying to compile a .cpp file that uses the coroutine library with the command.

clang-11 -std=c++20 -stdlib=libstdc++ main.cpp 

I get an error like this:

/usr/lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/coroutine:295:2: error: "the coroutine header requires -fcoroutines"
#error "the coroutine header requires -fcoroutines"

So, I add the flag:

clang-11 -std=c++20 -stdlib=libstdc++ main.cpp -fcoroutines

Now, I get the error:

clang-11: error: unknown argument: '-fcoroutines'

Is this a bug?

The closest question is here. However, I wasn’t able to conclude whether a bug exists or not.

For what its worth, here’s the source:

#include <iostream>
#include <coroutine>

template<typename T>
bool is_prime(T number) {
    for(int i=2;i<number;i++) {
        if (not i%number) return true;
    }
    return false;
}

class prime_iterator {
    unsigned int number = 2;
public:
    auto operator*() const {
        return number;
    }

    prime_iterator& operator++() {
        ++number;
        if (not is_prime(number)) {
            co_yield number;    // Trying to invoke co_yield just to see if library works.
        }
        return *this;
    }
};

auto main() -> int {
    for(prime_iterator p; *p < 30; ++p) {
        std::cout << *p << " is prime";
    }
}