cc/gcc: avoid passing --enable-multilib

Some versions of gcc have a broken --enable-multilib flag. As multilib is the
default, only pass the --disable-multilib flag

Signed-off-by: Cody P Schafer <dev@codyps.com>
[yann.morin.1998@free.fr: make it an if-block; duplicate commit log as comment]
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Message-Id: <5c970c1ceb22528fe28a.1399687923@localhost>
Patchwork-Id: 347585

 source "config/configure.in"

 source "config/backend.in"

 source "config/global.in"

 source "config/target.in"

 source "config/toolchain.in"

 source "config/kernel.in"

 source "config/binutils.in"

 source "config/cc.in"

 source "config/libc.in"

 source "config/debug.in"

 source "config/companion_libs.in"

 source "config/companion_tools.in"

 source "config/test_suite.in"