Implementation of IO with Panama

[Maurizio Cimadamore]

On 16/04/2021 15:10, Radosław Smogura wrote:
> I could grab address for it just looking for symbol from CLinker.
>
> But, AFIK, errno is thread local variable so maybe I should double check how this should be handled.


Interesting reading from man page:

```
errno  is  defined  by  the ISO C standard to be a modifiable lvalue of
        type int, and must not be explicitly declared; errno may be  a  
macro.
        errno  is  thread-local;  setting  it in one thread does not 
affect its
        value in any other thread.
```

this is subtle - it's an lvalue (e.g. can used e.g. for assignment) but 
is not explicitly declared - meaning it's not a variable in the proper 
sense.

At this point I'm not sure that linking to it gives the expected results.

In fact, firing up Godbolt shows that gcc uses __errno_location under 
the hood:

https://godbolt.org/z/rcMPTKxva

Maurizio