configure: Build GDB XML for 32 bit ARM CPUs into qemu aarch64 binaries

configure: Build GDB XML for 32 bit ARM CPUs into qemu aarch64 binaries

The qemu-aarch64 and qemu-system-aarch64 binaries include support
for all the 32 bit ARM CPUs as well as the 64 bit ones. This means
we need to build in the GDB XML files for the 32 bit CPUs too.
Otherwise gdb will complain:
 warning: while parsing target description (at line 1): Could not load XML document "arm-core.xml"
when you try to connect to our gdbserver to debug a 32 bit CPU
running in a qemu-aarch64 or qemu-system-aarch64 binary.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 1410533739-13836-1-git-send-email-peter.maydell@linaro.org