cc/gcc: disable complibs if not selected

Force gcc to not link with some companion libraries when
there are not needed (because selected-out).

There is no option to tell gcc *not* to build the Graphite and/or
LTO stuff. They *will* be built if gcc finds the suitable companion
libraries. If we do not provide them, but the host has them, then
gcc *will* find them, and link with them.

Consider the following:
- host has suitable PPL and CLooG (eg. Debian Squeeze)
- user wants to build gcc>=4.4
- user de-selects GRAPHITE
- gcc will find the hosts PPL and CLooG, and will use them
- the user moves the toolchain to an older host that does
not have them (eg. Debian Lenny)
- the toolchain fails, when it was properly setup not to

So, explicitly tell gcc *not* to use unneeded companion libs.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

 Original patch from Gentoo:

 gentoo/src/patchsets/binutils/2.19/03_all_binutils-2.15.92.0.2-ppc64-pie.patch

 diff -durN binutils-2.19.orig/bfd/elf64-ppc.c binutils-2.19/bfd/elf64-ppc.c

 --- binutils-2.19.orig/bfd/elf64-ppc.c	2008-10-09 14:18:24.000000000 +0200

 +++ binutils-2.19/bfd/elf64-ppc.c	2008-11-23 16:16:11.000000000 +0100

 @@ -11294,7 +11294,12 @@

  	      else if (!SYMBOL_REFERENCES_LOCAL (info, &h->elf)

  		       && !is_opd

  		       && r_type != R_PPC64_TOC)

 -		outrel.r_info = ELF64_R_INFO (h->elf.dynindx, r_type);

 +		{

 +		  outrel.r_info = ELF64_R_INFO (h->elf.dynindx, r_type);

 +		  if (h->elf.dynindx == -1

 +		      && h->elf.root.type == bfd_link_hash_undefweak)

 +		  memset (&outrel, 0, sizeof outrel);

 +		}

  	      else

  		{

  		  /* This symbol is local, or marked to become local,