add cgo example; fix zig url

test/BUILD

@@ -11,3 +11,5 @@ cc_binary(
     name = "exception",
     srcs = ["exception.cpp"],
 )
+
+# go build -ldflags "-linkmode external -extldflags -static" hello.go

test/hello.go

@@ -0,0 +1,9 @@
+package main
+
+// #include <stdio.h>
+// void helloworld() { printf("hello, world\n"); }
+import "C"
+
+func main() {
+	C.helloworld()
+}