For reasons discussed long ago and that have to do with how ld handles weak symbols, it was decided that it was preferable to link using an explicit list of object files, instead of adding object files to an archive first and then linking using this archive. This was applied for the CC2538, but not for CC13xx/CC26xx.
This pull applies this link logic to all CM3s. For this to work with the Contiki-NG build system, we need `.SECONDEXPANSION:`, so this pull moves that to the common CM3 Makefile.
This commit fixes two bugs related to the usage of MODULES for CC2538-based platforms:
* newlib is no longer under `lib/newlib` but under `os/lib/newlib`.
* There is no such thing as `sys` under `arm/common`, so this module is removed.
