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

 CT_EXPERIMENTAL=y

 CT_LOCAL_TARBALLS_DIR="${HOME}/src"

 CT_SAVE_TARBALLS=y

 CT_LOG_EXTRA=y

 CT_ARCH_CPU="cpu32"

 CT_ARCH_m68k=y

 CT_ARCH_BINFMT_FLAT=y

 CT_BINUTILS_V_2_20_1a=y

 CT_CC_V_4_3_4=y

 CT_LIBC_none=y

 CT_GMP_V_4_3_2=y

 CT_MPFR_V_2_4_2=y