fix cmake error

.travis.yml

@@ -42,7 +42,7 @@ before_install:
     function timeout() { perl -e 'alarm shift; exec @ARGV' "$@"; }
 script:
   - |
-    timeout 2580 paddle/scripts/travis/${JOB}.sh  # 43min timeout
+    timeout 2580 paddle/scripts/travis/${JOB}.sh -e "WITH_GOLANG=ON"  # 43min timeout
     RESULT=$?; if [ $RESULT -eq 0 ] || [ $RESULT -eq 142 ]; then true; else false; fi;
 notifications:
   email:

go/master/c/CMakeLists.txt

@@ -1 +1 @@
-go_library(paddle_master SHARED)
+go_library(paddle_master SHARED DEPS paddle_go_optimizer)

go/pserver/optimizer.go

@@ -2,7 +2,7 @@ package pserver
 
 // #cgo CFLAGS: -I ../../
 // //FIXME: ldflags contain "build" path
-// #cgo LDFLAGS: ../../build/go/pserver/client/c/libpaddle_go_optimizer.a -lstdc++
+// #cgo LDFLAGS: ../../build/go/pserver/client/c/libpaddle_go_optimizer.a -lstdc++ -lm
 // #include "paddle/optimizer/optimizer.h"
 // #include <stdlib.h>
 // #include <string.h>