Severin Teona - SAOC Milestone 3 Updates 2 & 3 - Druntime for Microcontrollers

[Severin Teona]

Hi guys, here are the updates 2 & 3 of the 3rd Milestone in 
#SAoC2020.

My last post is at [1]. My plan was:
- to continue building the DRuntime with the necessary modules;
- to solve the errors that could appear.

What I did was:
- continued adding the modules until there were no errors related 
to modules that were not imported;
- I got an error with an undefined reference to 'stderr'; this 
symbol is provided (on any other target) by the C standard 
library (the 'stderr', 'stdout' and 'stdin' symbols are defines 
using the 'extern' attribute in core/stdc/stdio.h);
- to solve the error, I started versioning the core/stdc/stdio.h 
and defined those symbols in the same way they are defined in 
newlib (I will probably import the newlib library later).
- I successfully compiled a TockOS application written in D and 
linked it with the DRuntime with no other errors; the final size 
of the DRuntime was around 1.7 MB which is a big improvement from 
the last final size (~2.5MB).
- I had problems with the emulator and lost some time configuring 
and installing different versions of the Renode emulator.

This week I am planning to do the following:
- solve the emulator problem, again, and hope to have a working 
testing environment;
- probably I will start versioning the DRuntime with this new 
architecture, if the application will run correctly on the 
emulator;
- if any errors appear, I will dig in my current setup to solve 
them.

[1]: 
https://forum.dlang.org/post/ldvbetlrenxwwhkygnbh@forum.dlang.org