complibs: split companion libraries to backend/frontend, a-la cc_core

Move the actual complibs codes to backend functions that builds the
required combo of build/host/target as requested by a frontend.

This split is currently a no-op, but is required for the upcoming
canadian-cross rework, where we'll be needing to build the complibs
twice, one for build/build, and one for build/host.

This applies to the six companion libraries:
- GMP
- MPFR
- PPL
- Cloog/PPL
- MPC
- libelf

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

 # ARM specific configuration file

 ## select ARCH_SUPPORTS_32

 ## select ARCH_DEFAULT_32

 ## select ARCH_SUPPORTS_BOTH_MMU

 ## select ARCH_DEFAULT_HAS_MMU

 ## select ARCH_SUPPORTS_BOTH_ENDIAN

 ## select ARCH_DEFAULT_LE

 ## select ARCH_SUPPORTS_WITH_ARCH

 ## select ARCH_SUPPORTS_WITH_CPU

 ## select ARCH_SUPPORTS_WITH_TUNE

 ## select ARCH_SUPPORTS_WITH_FLOAT

 ## select ARCH_SUPPORTS_WITH_FPU

 ## select ARCH_SUPPORTS_SOFTFP

 ##

 ## help The ARM architecture, as defined by:

 ## help     http://www.arm.com/