package/bind: disable backtrace support

package/bind: disable backtrace support

Disable backtrace support, fixes linking failure for uclibc/musl based
toolchains.

Fixes:

  - http://autobuild.buildroot.net/results/7a1a140314bc8d134f9eeb95ef2e46e7fb0ce9fd/

  .../arm-buildroot-linux-uclibcgnueabi/bin/ld: ../isc/.libs/libisc.so: undefined reference to `_Unwind_GetIP'

  - http://autobuild.buildroot.net/results/f0db5fe7fc6860b7270c784989c451e2e7aa2afb/

  .../arm-buildroot-linux-uclibcgnueabi/bin/ld: ../isc/.libs/libisc.so: undefined reference to `_Unwind_GetIP'

  - http://autobuild.buildroot.net/results/cb963298885df37f1e5c4d3ab3989773c01c54fc/

  .../arm-buildroot-linux-musleabihf/bin/ld: ../isc/.libs/libisc.so: undefined reference to `_Unwind_GetIP'

Signed-off-by: Peter Seiderer <ps.report@gmx.net>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>