Replace the branch to __cerror() in powerpc64 syscall stubs
with inline code which does what __cerror() was doing. #ifdef
that code (i.e. all code) out of cerror.S; __cerror() is no more.
This seems to be necessary to fix the link of rescue/rescue, and
should have the pleasant side effect of making all other workarounds
done to keep the 'b __cerror' working unnecessary.

Minimize differences between powerpc and powerpc64
Fix powerpc64 assembly to use right instructions for 64bit CPUs.
Use hidden for __curbrk and __minbrk to avoid GOT/TOC relocations.

branches: 1.5.4;
Pass PICFLAGS down to cc-as-as and use __PIC__ to decide if it is small
vs big PIC mode. Retire -DPIC and -DBIGPIC.

branches: 1.4.2;
PowerPC doesn't have CERROR since it never had a.out.
Use _C_LABEL(__cerror) instead.

Make __cerror protected to restore ABI leak in older libc versions,
where e.g. librt referenced the copy from libc. This still allows libc
to use PC-relative jumps.

branches: 1.2.2; 1.2.4;
Sync with other ports: in PIC mode make __cerror hidden; it is not supposed
to be used outside libc.

ppc64 build framework first pass