RocksDB build fails on riscv64

When building on RiscV64 on Ubuntu/Debian this fails due to missing libatomic fixes.

And example fromt he related bug/discussion at https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=933151:

/usr/bin/ld: librocksdblib.a(memtable.cc.o): in function `.L0 ':
./builddir/storage/rocksdb/./storage/rocksdb/rocksdb/util/dynamic_bloom.h:177:
undefined reference to `__atomic_fetch_or_1'
/usr/bin/ld: librocksdblib.a(memtable.cc.o): in function `.LVL1731':
./builddir/storage/rocksdb/./storage/rocksdb/rocksdb/util/dynamic_bloom.h:179:
undefined reference to `__atomic_fetch_or_1'
/usr/bin/ld: librocksdblib.a(memtable.cc.o): in function `SaveValue':
./builddir/storage/rocksdb/./storage/rocksdb/rocksdb/db/memtable.cc:596:
undefined reference to `__atomic_compare_exchange_1'
/usr/bin/ld: librocksdblib.a(memtable.cc.o): in function `.L0 ':
/usr/include/c++/8/bits/atomic_base.h:434: undefined reference to
`__atomic_compare_exchange_1'
/usr/bin/ld: /usr/include/c++/8/bits/atomic_base.h:434: undefined
reference to `__atomic_compare_exchange_1'
/usr/bin/ld: /usr/include/c++/8/bits/atomic_base.h:434: undefined
reference to `__atomic_compare_exchange_1'
/usr/bin/ld: /usr/include/c++/8/bits/atomic_base.h:434: undefined
reference to `__atomic_compare_exchange_1'
/usr/bin/ld: librocksdblib.a(memtable.cc.o):/usr/include/c++/8/bits/atomic_base.h:434:
more undefined references to `__atomic_compare_exchange_1' follow
collect2: error: ld returned 1 exit status