debug/gdb: disable nls when CT_TOOLCHAIN_ENABLE_NLS is not selected

Signed-off-by: Zhenqiang Chen <zhenqiang.chen@linaro.org>
Message-Id: <CACgzC7Bn+WpbgDruNeZ4s1z0x1deF6n4YyS22Dy7p_d1fFDVCA@mail.gmail.com>
PatchWork-Id: 191042

 reporter_name="Gustavo Zacarias <gustavo@zacarias.com.ar>"

 reporter_url="http://sourceware.org/ml/crossgcc/2011-03/msg00028.html"

 reporter_comment=""