Bug#962917: libatomic-ops: FTBFS in the testsuite on riscv64 due to missing -pthread

[Ivan Maidanski]

It would to solve the issue by adding -pthread because pthread-based 
implementation is not lock-free.
 
I have created the issue in upstream ( 
https://github.com/ivmai/libatomic_ops/issues/46 ).
By design of libatomic_ops, if a particular operation (e.g. 
__atomic_compare_exchange_1) is not supported by the CPU then the relevant AO 
primitive should not be defined (e.g. AO_char_compare_and_swap).
 
I could prepare the patch, but I don’t have access to the target architecture.