I wouldn't want to write using C as I prefer coding in assembly, you wouldn't happen to know of an assembly compiler for writing in PPC would you... 
Also have you ever heard of PPC680X0 from Coyote Flux, It was/is a 68K to PPC source-code convertor. I have two demo versions of this that were released in 1999 but I don't think a full package was ever released or completed (can't seem to find anything on the net about it though, the demos were found on an old 100% Amiga CD I used to subscribe to)...
gas (the gnu assembler) should support PPC. Personally I'd code in C though, because manually optimising code on a pipelined processor is quite hard. On a lot of recent processors it's quite hard to beat the compiler in some circumstances.
I met the coyote flux guys at a show when they were touting ppc680x0. It became free in 2004,
http://www.coyoteflux.nl/ I doubt they ever made any money on it.
They were pretty crazy guys, IIRC one of them had really mad hair. Pretty unlucky too, their last project for the GBA came out just after the DS.
