Hi Paul,
you're using CodeWarrior development tool to develop your application for MCP5668.
We've 2 versions supporting this device:
- CodeWarrior for MCU V10.5 based on Eclipse (most recent version),
- CodeWarrior for MPC55xx/56xx V2.10 based on classic IDE.
for my understanding the development tools don't include GCC build tool chain.
Under the compiler manual there is a chapter for GCC extensions.
Please have a look to "\CW MCU v10.5\MCU\Help\PDF\MCU_Power-Architecture_Compiler.pdf"
Page 283: Chapter 15 - C Compiler
We provide some header files for each processor.
this is used when you create a project with the wizard.
these files are in the folder:
\CW MCU v10.5\MCU\lib\wizard_data\PA\DataBase\derivatives
\CW for MPC55xx and MPC56xx 2.10\bin\Plugins\Support\MPC55XXWizard\DataBase\derivatives
We provide another tool which can be used to generate the config file for the processor used.
Details:
RAppID is a family of graphical development tools for the MPC5XXX family of Power Architecture® controllers that enables the user to quickly and easily configure the controller PLUS generate complete documentation. It can also be used as a learning tool to gain an understanding of the controller and it’s peripherals. RAppID not only generates C code for initializing the registers, but it also provides a system initialization function that brings the controller up in an orderly sequence. Use RAppID to save time and become an expert on the MPC5XXX Family.
Click on Download Tab and scroll down.
there is a version for:
RAppID Pin Wizard for MPC5668E/G processors 
: RAppID Pin Wizard for MPC5668G/E processors.
Size (K): 51223 Format: zip Rev #: 0 Modified: 2/27/2009
hope this will help you.
Regards
Pascal
