How to change which assembler GCC uses

[James Montgomerie]

I am porting GCC to a platform on which there is already a [free :-]
assembler and linker.  Currently, I'm just using gcc with -S to output
assembly and then running the assembler and linker manually.

I'm at the stage in development where I'd like to integrate the launching
of these programs with GCC, however they have a significantly different
command-line structure to their GNU equivalents on other platforms.  I
can't find anywhere in the GCC
documentation where it says whee to change the linking//assembling
command-line syntax for a platform.  Can someone point me in the right
direction? 

Thanks,
Jamie.