cc: add a flag for skipping core passes

It is used for skipping unnecessary compilation steps when the libc
doesn't need to be compiled (eg. when we do not use a C library).

Signed-off-by: Yann Diorcet <diorcet.yann@gmail.com>
Message-Id: <150eadb0117e697d79aa.1353625025@blackmint>
Patchwork-Id: 201222

 # 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