libgolang: Fix double C++ defer

If defer was used multiple times in one function it was failing to
compile. For example added test is failing like this:

    In file included from golang/runtime/libgolang_test.cpp:22:
    golang/runtime/libgolang_test.cpp: In function ‘void __test_defer(int*)’:
    ./golang/libgolang.h:457:59: error: redeclaration of ‘golang::_deferred _defer___COUNTER__’
     #define defer(f) golang::_deferred _defer_ ## __COUNTER__ (f)
                                                               ^
    golang/runtime/libgolang_test.cpp:473:5: note: in expansion of macro ‘defer’
         defer([&]() {
         ^~~~~
    ./golang/libgolang.h:457:36: note: ‘golang::_deferred _defer___COUNTER__’ previously declared here
     #define defer(f) golang::_deferred _defer_ ## __COUNTER__ (f)
                                        ^~~~~~~
    golang/runtime/libgolang_test.cpp:470:5: note: in expansion of macro ‘defer’
         defer([&]() {
         ^~~~~

It turns out the __COUNTER__ was not expanded and they say you have to
use 3 level of macro calls. Oh well...

https://stackoverflow.com/a/27611869/9456786

golang/libgolang.h

@@ -454,7 +454,9 @@ int select(const std::vector<_selcase> &casev) {
 
 // defer(f) mimics `defer f()` from golang.
 // NOTE contrary to Go f is called at end of current scope, not function.
-#define defer(f) golang::_deferred _defer_ ## __COUNTER__ (f)
+#define defer(f) golang::_deferred _defer_(__COUNTER__) (f)
+#define _defer_(counter)    _defer_2(counter)
+#define _defer_2(counter)   _defer_##counter
 struct _deferred {
     typedef func<void()> F;
     F f;

golang/runtime/libgolang_test.cpp

@@ -27,9 +27,11 @@
 #include <tuple>
 #include <utility>
 #include <string.h>
+#include <vector>
 using namespace golang;
 using std::move;
 using std::tie;
+using std::vector;
 
 #define __STR(X)  #X
 #define STR(X)    __STR(X)
@@ -466,16 +468,19 @@ void _test_select_inplace() {
 
 
 // verify that defer works.
-void __test_defer(bool *pcalled) {
+void __test_defer(vector<int> *pcalled) {
     defer([&]() {
-        *pcalled = true;
+        pcalled->push_back(1);
+    });
+    defer([&]() {
+        pcalled->push_back(2);
     });
     return;
 }
 void _test_defer() {
-    bool called = false;
+    vector<int> called, ok({2, 1});
     __test_defer(&called);
-    ASSERT(called);
+    ASSERT(called == ok);
 }