64-bit atomic load not implemented

[juj]

Trying to debug some code today with -sWASM=0 -pthread -sSAFE_HEAP, and I get

Assertion failed: (!curr->isAtomic && "64-bit atomic load not implemented"), function visitLoad, file /Users/clb/emsdk/binaryen/main/src/passes/I64ToI32Lowering.cpp, line 375.

The atomic operation comes from

 (func $SAFE_HEAP_LOAD_i64_1_A (param $0 i32) (param $1 i32) (result i64)

In this particular case I would not care even if 64-bit ops were atomic or not, so even if those were available as nonatomic, it would enable debugging the issue I am looking at.