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

CT_EXPERIMENTAL=y

CT_LOCAL_TARBALLS_DIR="${HOME}/src"

CT_SAVE_TARBALLS=y

CT_LOG_EXTRA=y

CT_ARCH_64=y

CT_ARCH_powerpc=y

CT_KERNEL_linux=y

CT_KERNEL_V_2_6_31_14=y

CT_BINUTILS_V_2_20_1a=y

CT_BINUTILS_FOR_TARGET=y

CT_CC_V_4_4_5=y

CT_CC_LANG_FORTRAN=y

CT_CC_LANG_CXX=y

CT_CC_LANG_JAVA=y

CT_LIBC_glibc=y

CT_LIBC_GLIBC_V_2_9=y

# CT_LIBC_GLIBC_FORCE_UNWIND is not set

CT_DEBUG_dmalloc=y

CT_DEBUG_duma=y

CT_DEBUG_gdb=y

CT_GDB_NATIVE=y

CT_GDB_V_6_8a=y

CT_DEBUG_strace=y

CT_STRACE_V_4_5_19=y

CT_GMP_V_5_0_1=y

CT_MPFR_V_3_0_0=y

CT_PPL_V_0_10_2=y

CT_CLOOG_V_0_15_10=y