[CIR][CIRGen] Atomics: handle atomic_compare_exchange_weak

[FantasqueX]

Traditional Clang implementation:

clangir/clang/lib/CodeGen/CGAtomic.cpp

Lines 545 to 550 in a0091e3

	case AtomicExpr::AO__c11_atomic_compare_exchange_weak:
	case AtomicExpr::AO__opencl_atomic_compare_exchange_weak:
	case AtomicExpr::AO__hip_atomic_compare_exchange_weak:
	emitAtomicCmpXchgFailureSet(CGF, E, true, Dest, Ptr, Val1, Val2,
	FailureOrder, Size, Order, Scope);
	return;