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 http://www.nabble.com/arm-linux-compilation-failure-and-possible-fix-td19229074.html

 diff -durN glibc-2.9.orig/ports/sysdeps/unix/sysv/linux/arm/sysdep.h glibc-2.9/ports/sysdeps/unix/sysv/linux/arm/sysdep.h

 --- glibc-2.9.orig/ports/sysdeps/unix/sysv/linux/arm/sysdep.h 25 Nov 2008 16:37:26 -0000 1.33

 +++ glibc-2.9/ports/sysdeps/unix/sysv/linux/arm/sysdep.h 27 Jan 2009 15:35:38 -0000

 @@ -28,6 +28,8 @@

  /* Defines RTLD_PRIVATE_ERRNO and USE_DL_SYSINFO.  */

  #include <dl-sysdep.h>

 +#include <tls.h>

 +

  /* For Linux we can use the system call table in the header file

 	/usr/include/asm/unistd.h

     of the kernel.  But these symbols do not follow the SYS_* syntax