[clang][bytecode] Clang produces incorrect mutable lambda code in presence of `-fexperimental-new-constant-interpreter`

[BobIsOnFire]

Minimal repro:

#include <iostream>

int main() {
    auto foo = [a = false]() mutable {
        if (a) std::cout << ',';
        a = true;
        std::cout << 'A';
    };

    foo();
    foo();
}

https://godbolt.org/z/6nn4z4eqM

Looks like when -fexperimental-new-constant-interpreter is set, if (a) condition is optimized away completely, and -Wunreachable-code warning is emitted.

Didn't find anything similar in "clang:bytecode" open issues, but feel free to close if this is a duplicate.

[tbaederr]

Yup, the read from a incorrectly succeeds and the first std::cout just vanishes.