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>

 alpha does not have a __NR_creat

 http://bugs.gentoo.org/227275

 http://sourceware.org/bugzilla/show_bug.cgi?id=6650

 diff -durN glibc-2.10.1.orig/sysdeps/unix/sysv/linux/wordsize-64/creat64.c glibc-2.10.1/sysdeps/unix/sysv/linux/wordsize-64/creat64.c

 --- glibc-2.10.1.orig/sysdeps/unix/sysv/linux/wordsize-64/creat64.c	2007-11-10 20:34:26.000000000 +0100

 +++ glibc-2.10.1/sysdeps/unix/sysv/linux/wordsize-64/creat64.c	2009-11-13 00:50:51.000000000 +0100

 @@ -1 +1,5 @@

  /* Defined as alias for the syscall.  */

 +#include <sysdep.h>

 +#ifndef __NR_creat

 +#include "../../../../../io/creat64.c"

 +#endif