Hacky ARM64 atomics in Jai

Atomics.jai

    // ARM64 hack: Unlike x64, even though aligned reads are atomic, ARM64 doesn't guarantee acquire semantics with
    //             normal reads and release semantics with normal stores. There are separate instructions for those,
    //             and since we don't have ARM64 inline assembly yet, we must implement them with this very very spooky
    //             hack where we hardcode the machine instructions we want. The parameters are assumed to be passed
    //             according to Jai's current LLVM ABI!
    //             Thanks @ctpeepee!
    atomic_read :: no_inline (pointer: *s64) -> s64 {
        // ldr  x1, [x1]    x1 initially contains a pointer to "pointer", which itself is a pointer
        // ldar x1, [x1]
        // str  x1, [x2]    x2 here contains a pointer to the first return value.
        defer #bytes .[0x21, 0x00, 0x40, 0xF9, 0x21, 0xFC, 0xDF, 0xC8, 0x41, 0x00, 0x00, 0xF9];
        return 0;
    }

    atomic_write :: no_inline (pointer: *s64, new_value: s64) {
        // ldr  x2, [x2]    x2 initially contains a pointer to "new_value"
        // ldr  x1, [x1]    x1 initially contains a pointer to "pointer", which itself is a pointer
        // stlr x2, [x1]
        #bytes .[0x42, 0x00, 0x40, 0xF9, 0x21, 0x00, 0x40, 0xF9, 0x22, 0xFC, 0x9F, 0xC8];
    }