FTBFS in the testsuite on riscv64 about libatomic_ops

[ivmai]

It would be wrong to solve the issue by adding -pthread because pthread-based implementation is not lock-free.

[ivmai]

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.

[ivmai]

Undefined references in the given build:
__atomic_compare_exchange_1
__atomic_compare_exchange_2
__atomic_fetch_add_1
__atomic_fetch_add_2
__atomic_fetch_and_1
__atomic_fetch_and_2
__atomic_fetch_or_1
__atomic_fetch_or_2
__atomic_fetch_xor_1
__atomic_fetch_xor_2

[ivmai]

The comment in gcc/riscv.h seems to be incorrect:
/* As of gcc-7.2.0, some __GCC_HAVE_SYNC_COMPARE_AND_SWAP_n are missing. /
/ The operations are lock-free (even for the types smaller than word). */
#define AO_GCC_FORCE_HAVE_CAS

[ivmai]

Related issue: #31

[ivmai]

As said in #31, byte-width and short-width atomic operations are supported and lock-free but gcc requires -latomic currently (unlike clang).