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>

 Dmitry V. Levin [Tue, 3 Nov 2009 16:49:49 +0000]

 Fix check for linux/netlink.h on Linux 2.6.32-rc5+

 * configure.ac (AC_CHECK_HEADERS): In check for linux/netlink.h, include 

   sys/socket.h instead of linux/socket.h beforehand.

 diff --git a/configure.ac b/configure.ac

 --- a/configure.ac

 +++ b/configure.ac

 @@ -258,7 +258,7 @@ AC_CHECK_HEADERS([ \

  ], [], [])

  AC_CHECK_HEADERS([linux/icmp.h linux/in6.h linux/netlink.h linux/if_packet.h],

                   [], [], [#include <stddef.h>

 -#include <linux/socket.h>])

 +#include <sys/socket.h>])

  AC_CHECK_HEADERS([asm/sigcontext.h], [], [], [#include <signal.h>])

  AC_CHECK_TYPES([struct sigcontext_struct,

  		struct sigcontext],,, [#include <signal.h>])