tools/nolibc: add support for constructors and destructors

With the startup code moved to C, implementing support for
constructors and deconstructors is fairly easy to implement.

Examples for code size impact:

   text	   data	    bss	    dec	    hex	filename
  21837	    104	     88	  22029	   560d	nolibc-test.before
  22135	    120	     88	  22343	   5747	nolibc-test.after
  21970	    104	     88	  22162	   5692 nolibc-test.after-only-crt.h-changes

The sections are defined by [0].

[0] https://refspecs.linuxfoundation.org/elf/gabi4+/ch5.dynamic.html



Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Acked-by: Willy Tarreau <w@1wt.eu>
Link: https://lore.kernel.org/lkml/20231007-nolibc-constructors-v2-1-ef84693efbc1@weissschuh.net/