Added dummy retargeting for the SYS IO functions

[marcoaccame]

This PR adds retargeting of the system IO functions, so that we can use the armclang compiler with versions > v6.19.

The addition of these functions is required because:

• I noticed that if we used compiler v 6.20 and beyond the applications when debugged stepped in several breakpoints before entering in main(). And even worse, when not in debug it did not bootstrap;
• So, we have made sure to use V6.19 and I started an investigation.
• It ended up that it was responsibility of the compiler because (from ARM):

  ... since the change [SDCOMP-64440] described in the release note of v6.22 https://developer.arm.com/documentation/109472/6-22/?lang=en
  Such a change seems to make armlink to link many additional Arm C/C++ standard lib components like printf, vfprintf or abort etc.
  When your debug session stuck at breakpoint 0xAB, usually it indicates a semihosting issue: https://developer.arm.com/documentation/ka002219/latest/

• told that they would have fixed this:

  Hi Marco, our compiler team has confirmed this is indeed something we should investigate further and implement some improvement if possible.

• and in the meantime thy suggested as a quick workaround:

  I know how to get rid of the debug issue caused by the unexpected semihosting. You can implement your own retarget file or use the one provided in the Arm::CMSIS-Compiler pack as described on the page I sent you.

So, in here I add the workaround.

I have added the functions in two existing files files that are used by all the projects, so that we don't need to change a humongous number of projects:

• EOMtheSystem.c for the legacy projects (ems, ...)
• embot_hw_sys.cpp for the embot projects.

And I have reverted some projects for the use of the installed compiler version.

I have tested the changes w/ some boards and everything works fine.