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

diff -durN gcc-4.4.4.orig/boehm-gc/include/gc.h gcc-4.4.4/boehm-gc/include/gc.h

--- gcc-4.4.4.orig/boehm-gc/include/gc.h	2007-04-23 23:10:09.000000000 +0200

+++ gcc-4.4.4/boehm-gc/include/gc.h	2010-05-16 19:36:48.000000000 +0200

@@ -503,7 +503,7 @@

 #if defined(__linux__) || defined(__GLIBC__)

 # include <features.h>

 # if (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 1 || __GLIBC__ > 2) \

-     && !defined(__ia64__)

+     && !defined(__ia64__) && !defined(__UCLIBC__)

 #   ifndef GC_HAVE_BUILTIN_BACKTRACE

 #     define GC_HAVE_BUILTIN_BACKTRACE

 #   endif