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>

 Original patch from H.J. Lu, as reported there:

 http://www.nabble.com/PATCH:-Use-short-for-fnstsw-td14775171.html

 fnstsw stores 16bit into %ax. The upper 16bit of %eax is unchanged.

 The new assembler (binutils-2.18.50.0.4 and up) will disallow "fnstsw %eax".

 diff -dur glibc-2.6.1.orig/sysdeps/i386/fpu/ftestexcept.c glibc-2.6.1/sysdeps/i386/fpu/ftestexcept.c

 --- glibc-2.6.1.orig/sysdeps/i386/fpu/ftestexcept.c	2004-03-05 11:14:48.000000000 +0100

 +++ glibc-2.6.1/sysdeps/i386/fpu/ftestexcept.c	2008-06-24 10:56:14.000000000 +0200

 @@ -26,7 +26,7 @@

  int

  fetestexcept (int excepts)

  {

 -  int temp;

 +  short temp;

    int xtemp = 0;

    /* Get current exceptions.  */