Fixing win32 build.

Author: Eric Holk

src/rt/arch/i386/_context.S

@@ -78,7 +78,7 @@ swap_registers:
 .globl task_trampoline
 task_trampoline:
     // This gets set up by std::task::_spawn.
-#ifdef __APPLE__
+#if defined(__APPLE__) || defined(__WIN32__)
     call _task_exit
 #else
     call task_exit