package/rocksdb: fix C++ tests

This will fix a build failure on xtensa and nios2 that missed
-faligned-new

Fixes:
 - http://autobuild.buildroot.org/results/58bf25a16984c4d5f3ce0e26a56712410b67c53a
 - http://autobuild.buildroot.org/results/718fee3d20ef00ffa5c3e617a036cf2b82c97411



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>