title: why report the error " undefined reference to `add2" when I used cgo
body: <p>The directory is follow:<br>
  -inlcude<br>
  Test.h<Br>
  -lib<br>
  libmytest.so<br>
  -src<br>
  test.go<Br></p>
  
  <p>The test.go code is follow:<br></p>
  
  <pre><code>package main
  
  /*
  #cgo CFLAGS : -I ../include
  #cgo LDFLAGS: -L ../lib -lmytest
  #include "Test.h"
  */
  import "C"
  func main() {
      C.add2(10, 10)
  }
  </code></pre>
  
  <p>When I use <code>go build test.go</code>, the console report that: # command-line-arguments
  /tmp/go-build168903458/command-line-arguments/_obj/test.cgo2.o: In function <code>_cgo_9efddd4c1a4b_Cfunc_add2':
  rocketmq-bridge/src/cgo-gcc-prolog:42: undefined reference to</code>add2'
  collect2: error: ld returned 1 exit status</p>