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/2.19/76_all_use-new-ld-dtags.patch

 diff -durN binutils-2.19.orig/ld/ldmain.c binutils-2.19/ld/ldmain.c

 --- binutils-2.19.orig/ld/ldmain.c	2008-11-23 16:54:42.000000000 +0100

 +++ binutils-2.19/ld/ldmain.c	2008-11-23 16:56:16.000000000 +0100

 @@ -262,6 +262,7 @@

    link_info.allow_undefined_version = TRUE;

    link_info.keep_memory = TRUE;

 +  link_info.new_dtags = TRUE;

    link_info.combreloc = TRUE;

    link_info.strip_discarded = TRUE;

    link_info.emit_hash = TRUE;