package/dc3dd: disable on riscv32

package/dc3dd: disable on riscv32

Disable dc3dd on riscv32 because of the size of time_t (riscv32 has
never had a 32-bit time, and has always been 64-bit from the onset):

        In file included from getdate.y:40:
        verify.h:132:30: error: negative width in bit-field 'verify_error_if_negative_size__'
          132 |       (struct { unsigned int verify_error_if_negative_size__: (R) ? 1 : -1; }))
              |                              ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
        verify.h:138:61: note: in expansion of macro 'verify_true'
          138 | # define verify(R) extern int (* verify_function__ (void)) [verify_true (R)]
              |                                                             ^~~~~~~~~~~
        getdate.y:116:1: note: in expansion of macro 'verify'
          116 | verify (LONG_MIN <= TYPE_MINIMUM (time_t) && TYPE_MAXIMUM (time_t) <= LONG_MAX);
              | ^~~~~~

Fixes:
 - http://autobuild.buildroot.org/results/267151dec9d2328a5f8c61ddf224219a4f617e5c

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>