>> In file included from drivers/i2c/algos/i2c-algo-bit.c:31:
>> include/linux/i2c.h:58: error: array type has incomplete element type
>> include/linux/i2c.h:197: error: array type has incomplete element
>> type
>> It's very important that standard-kernel should compile on FC4....
>
> Its a bug in the base kernel. gcc 4 is just spotting a long standing
> error in the code that previous compilers missed. This is a known
> problem in the
> 2.6.11 base kernels but isn't considered security critical so hasn't
> been fixed in 2.6.11.x yet

I had the exact same type of problem in FC4T2, I googled it and found it to be pretty common. The solution is to replace your version of i2c.h with a modified one that has proper function defs.  Once I replaced it, I was able to compile my new kernels.  Give me some time and I will look for it again.

-Joshua Liebowitz