compiler: fix passing weirdly-padded structs to new goroutines

The values were stored in the passed object as the values itself (not
expanded like is common in the calling convention), and read back after
assuming they were expanded. This often works for simple parameters
(int, pointer, etc), but not for more complex parameters. Especially
when there's padding.

Found this while working on `//go:wasmexport`.

compiler/goroutine.go

@@ -49,7 +49,7 @@ 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.getValue(param, getPos(instr)))
+		params = append(params, b.expandFormalParam(b.getValue(param, getPos(instr)))...)
 	}
 
 	var prefix string