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>

 Index: binutils-2.19.51.0.5/ld/ld.texinfo

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

 --- binutils-2.19.51.0.5.orig/ld/ld.texinfo

 +++ binutils-2.19.51.0.5/ld/ld.texinfo

 @@ -2036,8 +2036,9 @@ This linker can create the new dynamic t

  systems may not understand them. If you specify

  @option{--enable-new-dtags}, the dynamic tags will be created as needed.

  If you specify @option{--disable-new-dtags}, no new dynamic tags will be

 -created. By default, the new dynamic tags are not created. Note that

 -those options are only available for ELF systems.

 +created. On Gentoo, by default, the new dynamic tags are created (this

 +differs from upstream behaviour). Note that those options are only

 +available for ELF systems.

  @kindex --hash-size=@var{number}

  @item --hash-size=@var{number}