crosstool: add EXPAT as a dependency on the gdb build.

qemu-power8 wants to tell about itself with XML, and so
we need to build gdb with EXPAT so it can understand XML.

Change-Id: I460e27f883956ed5d54e6070916e2682ee0f7a1b
Signed-off-by: Ronald G. Minnich <rminnich@gmail.com>
Reviewed-on: https://review.coreboot.org/13846
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Reviewed-by: Martin Roth <martinroth@google.com>

util/crossgcc/buildgcc

@@ -627,9 +627,10 @@ case "$PACKAGE" in
 		;;
 	GDB|gdb)
 		NAME="${TARGETARCH} cross GDB"
-		PACKAGES="GDB"
 		if [ $SKIPPYTHON -eq 0 ]; then
-			PACKAGES="EXPAT PYTHON $PACKAGES"
+			PACKAGES="EXPAT PYTHON GDB"
+		else
+			PACKAGES="EXPAT GDB"
 		fi
 		;;
 	CLANG|clang)