Upgrade to Go 1.18 and re-vendor dependencies

vendor/golang.org/x/sys/windows/dll_windows.go

@@ -32,6 +32,8 @@ type DLLError struct {
 
 func (e *DLLError) Error() string { return e.Msg }
 
+func (e *DLLError) Unwrap() error { return e.Err }
+
 // A DLL implements access to a single DLL.
 type DLL struct {
 	Name   string
@@ -389,7 +391,6 @@ func loadLibraryEx(name string, system bool) (*DLL, error) {
 	var flags uintptr
 	if system {
 		if canDoSearchSystem32() {
-			const LOAD_LIBRARY_SEARCH_SYSTEM32 = 0x00000800
 			flags = LOAD_LIBRARY_SEARCH_SYSTEM32
 		} else if isBaseName(name) {
 			// WindowsXP or unpatched Windows machine