[WebAssembly] Fix __builtin_wasm_tls_base intrinsic

[quantum]

Summary

Properly generate the outchain for the __builtin_wasm_tls_base intrinsic.

Also marked the intrinsic pure, per @sunfish's suggestion.

[tlively]

LGTM modulo a test!

[quantum]

Add a test with a memory dependency on __builtin_wasm_tls_base.

clang/include/clang/Basic/BuiltinsWebAssembly.def

 BUILTIN(__builtin_wasm_memory_grow, "zIiz", "n")
 
 // Bulk memory builtins
 TARGET_BUILTIN(__builtin_wasm_memory_init, "vIUiIUiv*UiUi", "", "bulk-memory")
 TARGET_BUILTIN(__builtin_wasm_data_drop, "vIUi", "", "bulk-memory")
 
 // Thread-local storage
 TARGET_BUILTIN(__builtin_wasm_tls_size, "z", "nc", "bulk-memory")
-TARGET_BUILTIN(__builtin_wasm_tls_base, "v*", "n", "bulk-memory")
+TARGET_BUILTIN(__builtin_wasm_tls_base, "v*", "nU", "bulk-memory")
 
 // Floating point min/max
 BUILTIN(__builtin_wasm_min_f32, "fff", "nc")
 BUILTIN(__builtin_wasm_max_f32, "fff", "nc")
 BUILTIN(__builtin_wasm_min_f64, "ddd", "nc")
 BUILTIN(__builtin_wasm_max_f64, "ddd", "nc")
 
 // Exception handling builtins.

llvm/lib/Target/WebAssembly/WebAssemblyISelDAGToDAG.cpp

void WebAssemblyDAGToDAGISel::Select(SDNode *Node) {
   case ISD::INTRINSIC_W_CHAIN: {
     unsigned IntNo = cast<ConstantSDNode>(Node->getOperand(1))->getZExtValue();
     switch (IntNo) {
     case Intrinsic::wasm_tls_base: {
       MVT PtrVT = TLI->getPointerTy(CurDAG->getDataLayout());
       assert(PtrVT == MVT::i32 && "only wasm32 is supported for now");
 
       MachineSDNode *TLSBase = CurDAG->getMachineNode(
-          WebAssembly::GLOBAL_GET_I32, DL, MVT::i32,
+          WebAssembly::GLOBAL_GET_I32, DL, MVT::i32, MVT::Other,
           CurDAG->getTargetExternalSymbol("__tls_base", PtrVT),
           Node->getOperand(0));
       ReplaceNode(Node, TLSBase);
       return;
     }
     }
     break;
   }