package/dieharder: fix build with gcc 10

Disable -fno-common with dieharder, there is more than 100 variables to
fix and upstream seems dead.

Fixes:
 - http://autobuild.buildroot.org/results/ba70d111cd1f2029a193a88af3b44daf6ef27786



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