Compiling ports in a post-9.0-RELEASE world

[Marco van de Voort]

In our previous episode, Matthias Andree said:
> 
> So far I've found clang surprisingly good in that it revealed a few 
> quirks in my own software (in C) that GCC or ICC had silently accepted, 
> and the static analyzer has a few rough edges, but I have found bugs in 
> my own software, not in clang 2.8 so far, although I suspect that a few 
> might linger there.

How much changes for non-(GC)C ports? In other words, ports that directly
use AS and LD to generate binaries, but might also link to C libraries
outside of gcc's control.

(I'm thinking about e.g. lang/fpc here)

Issues like

- Are there fundamental startup code (CSU) changes due to this in 9?
- libraries that might need to be implicitely linked when linking against C
  code (like libgcc,c)
- Do certain libc internal macros change (like __errno_location)
- Do lowlevel details of stuff like TLS change?

Of course I'll load up some RC or DP in a VM if necessary to find my own
answers. But if somebody knows some details, it would help guestimating the
effort.