Pass PICFLAGS down to cc-as-as and use __PIC__ to decide if it is small
vs big PIC mode. Retire -DPIC and -DBIGPIC.

add a weak alias from ffs to __ffssi2. sparc dynamic works with gcc 4.5 now.

Don't export __ffstab, it's used only in this routine. This gets
rid of one of those evil common symbols in the __ namespace.

reviewed by martin

Merge libkern + libc common files. As requested by core.