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>

 diff -durN ltrace-0.4.orig/configure ltrace-0.4/configure

 --- ltrace-0.4.orig/configure	2008-10-23 23:19:38.000000000 +0200

 +++ ltrace-0.4/configure	2008-10-23 23:19:06.000000000 +0200

 @@ -1392,6 +1392,9 @@

  HOST_OS="$host_os"

 +case "${HOST_OS}" in

 +  linux-*) HOST_OS=linux-gnu;;

 +esac

  ac_ext=c

 diff -durN ltrace-0.4.orig/configure.ac ltrace-0.4/configure.ac

 --- ltrace-0.4.orig/configure.ac	2008-10-23 23:19:43.000000000 +0200

 +++ ltrace-0.4/configure.ac	2008-10-23 23:18:44.000000000 +0200

 @@ -7,6 +7,9 @@

  dnl Check host system type

  AC_CANONICAL_HOST

  HOST_OS="$host_os"

 +case "${HOST_OS}" in

 +  linux-*) HOST_OS=linux-gnu;;

 +esac

  AC_SUBST(HOST_OS)

  dnl Checks for programs.