cc/gcc: pass the companion libs prefix to cc_core

In case of canadian-cross, the companion libraries are not the same for
the core cc (they run on 'build') as they are for the final cc (they run
on 'host').

Prepare for this differentiation (coming later), while retaining the
current behavior (to use the same compblibs).

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

 # m68k specific configuration file

 ## depends on EXPERIMENTAL

 ##

 ## select ARCH_SUPPORTS_32

 ## select ARCH_DEFAULT_32

 ## select ARCH_DEFAULT_BE

 ## select ARCH_SUPPORTS_WITH_CPU

 ##

 ## help The m68k architecture