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: mpf_set_str.c.4.diff

 -= BEGIN original header =-

 -= END original header =-

 diff -durN gmp-4.2.4.orig/mpf/set_str.c gmp-4.2.4/mpf/set_str.c

 --- gmp-4.2.4.orig/mpf/set_str.c	2008-08-25 16:11:37.000000000 +0200

 +++ gmp-4.2.4/mpf/set_str.c	2009-03-08 18:36:16.000000000 +0100

 @@ -137,7 +137,12 @@

        c = (unsigned char) *++str;

      }

 +  /* Default base to decimal.  */

 +  if (base == 0)

 +    base = 10;

 +

    exp_base = base;

 +

    if (base < 0)

      {

        exp_base = 10;

 @@ -165,10 +170,6 @@

  	return -1;

      }

 -  /* Default base to decimal.  */

 -  if (base == 0)

 -    base = 10;

 -

    /* Locate exponent part of the input.  Look from the right of the string,

       since the exponent is usually a lot shorter than the mantissa.  */

    expptr = NULL;