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>

 # Menu for the cross GDB

 config GDB_CROSS

     bool

     prompt "Cross-gdb"

     default y

     select GDB_GDBSERVER if ! BARE_METAL

     help

       Build and install a cross-gdb for the target, to run on host.

 if GDB_CROSS

 config GDB_CROSS_STATIC

     bool

     prompt "Build a static cross gdb"

     default n

     help

       A static cross gdb can be usefull if you debug on a machine that is

       not the one that is used to compile the toolchain.

       That way, you can share the cross-gdb without installing a toolchain

       on every machine that will be used to debug target programs.

 endif # GDB_CROSS