compiler: centralize loads and stores of SSA values

Map, channel, index, and goroutine lowering each create allocas, store
SSA values into them, load results, and emit lifetime intrinsics.

Add helpers for these operations and use runtimeValueResult for runtime
calls that write a value and an optional comma-ok result. The generated
LLVM IR is unchanged.

compiler/goroutine.go

@@ -50,7 +50,7 @@ func (b *builder) createGo(instr *ssa.Go) {
 	// Get all function parameters to pass to the goroutine.
 	var params []llvm.Value
 	for _, param := range instr.Call.Args {
-		params = append(params, b.expandFormalParam(b.getValue(param, getPos(instr)))...)
+		params = append(params, b.getGoroutineCallArgument(param)...)
 	}
 
 	var prefix string
@@ -122,6 +122,10 @@ func (b *builder) createGo(instr *ssa.Go) {
 	b.createCall(fnType, start, []llvm.Value{callee, paramBundle, stackSize, llvm.Undef(b.dataPtrType)}, "")
 }
 
+func (b *builder) getGoroutineCallArgument(value ssa.Value) []llvm.Value {
+	return b.expandFormalParam(b.getValue(value, getPos(value)))
+}
+
 // Create an exported wrapper function for functions with the //go:wasmexport
 // pragma. This wrapper function is quite complex when the scheduler is enabled:
 // it needs to start a new goroutine each time the exported function is called.