scripts/gdb: If not building expat for gdb, disable

--with-expat=yes is unconditionally passed to the gdb configure
stage, instead of respecting the ${do_expat} decision.

Disable if not needed. Prevents error building canadian cross;

configure: error: expat is missing or unusable

Where configure stage fails to find expat on the host compiler.

Signed-off-by: "David Holsgrove" <david.holsgrove@xilinx.com>
Signed-off-by: Bryan Hundven <bryanhundven@gmail.com>
Message-Id: <4c4410a2a8aab24a29c5.1349244128@localhost.localdomain>
PatchWork-Id: 188711

# Compute microblaze specific values

CT_DoArchTupleValues () {

    # The architecture part of the tuple:

    CT_TARGET_ARCH="${CT_ARCH}${target_endian_el}"

    # gcc ./configure flags

    CT_ARCH_WITH_ARCH=

    CT_ARCH_WITH_ABI=

    CT_ARCH_WITH_CPU=

    CT_ARCH_WITH_TUNE=

    CT_ARCH_WITH_FPU=

    CT_ARCH_WITH_FLOAT=

    # CFLAGS

    case "${CT_ARCH_FLOAT_HW},${CT_ARCH_FLOAT_SW}" in

        y,) CT_ARCH_FLOAT_CFLAG="-mhard-float" ;;

        ,y) CT_ARCH_FLOAT_CFLAG="-msoft-float" ;;

    esac

}