package/bitcoin: unset the NDEBUG flag

package/bitcoin: unset the NDEBUG flag

Since https://git.buildroot.net/buildroot/commit/?id=5a8c50fe05afacc3cbe8e7347e238da9f242fab0
all packages are now built with NDEBUG, which broke Bitcoin builds.

Bitcoin is using assert(...) extensively with the assumption of it
never being a noop at runtime. So we cannot build with NDEBUG.
See: https://github.com/bitcoin/bitcoin/blob/0.21/src/compat/assumptions.h

Fixes:
    http://autobuild.buildroot.org/results/83b/83b6dc0b97b19888fb1187bbbca485961e58ce90/
    and so many more...

Signed-off-by: Dick Olsson <hi@senzilla.io>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>