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>

This is backported partially from 2.20 branch

http://sourceware.org/ml/binutils-cvs/2009-10/msg00173.html

-Khem

Index: binutils-2.20/gas/as.h

===================================================================

--- binutils-2.20.orig/gas/as.h	2009-10-22 00:27:08.700469349 -0700

+++ binutils-2.20/gas/as.h	2009-10-22 00:28:04.068416318 -0700

@@ -238,7 +238,7 @@ typedef addressT valueT;

 #define know(p) gas_assert(p)	/* Verify our assumptions!  */

 #endif /* not yet defined */

 #else

-#define know(p)			/* know() checks are no-op.ed  */

+#define know(p) do {} while (0)	/* know() checks are no-op.ed  */

 #endif

 /* input_scrub.c */