You don't need the -( -) here, FWIW. libgcc does not require symbols from coreboot.a ;-)
Yes, actually it does. On powerpc libgcc uses external symbols that it does not provide.
Do you mean abort()? Yeah, you need to provide that yourself, on all targets (nothing special about PowerPC); the same is true for memcpy(), memset (), memmove(), memcmp(). FWIW, any GCC-compiled code can require those, not only code in libgcc.
Segher