test: fix _embdemo

_embdemo/write-esp32/main.go

@@ -0,0 +1,12 @@
+package main
+
+import "github.com/goplus/lib/c"
+
+func main() {
+	buf := c.Malloc(6)
+	c.Memset(buf, 0, 6)
+	c.Strncpy((*c.Char)(buf), c.Str("abcde"), 5)
+
+	write(1, (*c.Char)(buf), 5)
+
+}