fix generic panic, add movbe check

cpuid.go

@@ -0,0 +1,12 @@
+//go:build amd64
+// +build amd64
+
+package base14
+
+func cpuid(op uint32) (eax, ebx, ecx, edx uint32)
+
+// True when MOVBEx instructions are available.
+var movbe = func() bool {
+	_, _, c, _ := cpuid(1)
+	return c&(1<<22) > 0
+}()