First, please mention which CPU you are targeting. I make an educated guess and assume you are targeting a S12X and you are using the XGATE.
The XGATE compiler does prefix its functions with __X_.
In general I would recommend to create a project with the new project wizard and see how the newly generated project it setup, it does include the right libraries for example.
In your case, the XGATE runtime routines are defined in the XGATE libraries,
See
C:\Program Files\Freescale\CodeWarrior for HCS12 V4.7\lib\xgatec\readme.txt for a list,
you probably want to use the integer only lib:
C:\Program Files\Freescale\CodeWarrior for HCS12 V4.7\lib\xgatec\lib\ansi_xgi.lib
The actual IMULU/IDIVU runtime routines are implemented in
C:\Program Files\Freescale\CodeWarrior for HCS12 V4.7\lib\xgatec\src\rtsxgate.cxgate
You can alternatively to the library also add this source file to your project, but then only the runtime routines and not all the ANSI functions are available.
Daniel