refactor(windows): split Windows code into winapi (#575)

crypto/windows/payload/stub_windows.go

@@ -0,0 +1,15 @@
+//go:build windows && !abe_embed
+
+package payload
+
+import "fmt"
+
+// Get returns an error in non-release builds so feature code that needs
+// the payload fails fast with a clear message. Release builds (built
+// with -tags abe_embed) replace this with the //go:embed'd binary.
+func Get(arch string) ([]byte, error) {
+	return nil, fmt.Errorf(
+		"abe: payload not embedded in this build (rebuild with -tags abe_embed; arch=%s)",
+		arch,
+	)
+}