Export modules' DSO constructors.

We need to reference DSO constructors to make sure they can actually be
linked to the final binary, see http://git.io/DRIqCg.

src/node.h

@@ -402,14 +402,14 @@ extern "C" NODE_EXTERN void node_module_register(void* mod);
 #if defined(_MSC_VER)
 #pragma section(".CRT$XCU", read)
 #define NODE_C_CTOR(fn)                                               \
-  static void __cdecl fn(void);                                       \
+  void __cdecl fn(void);                                              \
   __declspec(dllexport, allocate(".CRT$XCU"))                         \
       void (__cdecl*fn ## _)(void) = fn;                              \
-  static void __cdecl fn(void)
+  void __cdecl fn(void)
 #else
 #define NODE_C_CTOR(fn)                                               \
-  static void fn(void) __attribute__((constructor));                  \
-  static void fn(void)
+  void fn(void) __attribute__((constructor));                         \
+  void fn(void)
 #endif
 
 #define NODE_MODULE_X(modname, regfunc, priv, flags)                  \