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>

 --- gcc-4.2.1-stock/gcc/config/alpha/linux-unwind.h	2005-06-24 20:22:41.000000000 -0500

 +++ gcc-4.2.1/gcc/config/alpha/linux-unwind.h	2007-09-01 20:21:34.000000000 -0500

 @@ -29,6 +29,9 @@ Boston, MA 02110-1301, USA.  */

  /* Do code reading to identify a signal frame, and set the frame

     state data appropriately.  See unwind-dw2.c for the structs.  */

 +/* Don't use this if inhibit_libc is set

 +   The build for this target will fail trying to include missing headers */

 +#ifndef inhibit_libc

  #include <signal.h>

  #include <sys/ucontext.h>

 @@ -80,3 +83,4 @@ alpha_fallback_frame_state (struct _Unwi

    fs->retaddr_column = 64;

    return _URC_NO_REASON;

  }

 +#endif /* inhibit_libc */