Rewrite async_exec_lock using mpscq
diff --git a/binding.gyp b/binding.gyp
index ccd811a..9d04eb9 100644
--- a/binding.gyp
+++ b/binding.gyp
@@ -520,6 +520,7 @@
         'src/core/lib/support/murmur_hash.c',
         'src/core/lib/support/slice.c',
         'src/core/lib/support/slice_buffer.c',
+        'src/core/lib/support/stack_lockfree.c',
         'src/core/lib/support/string.c',
         'src/core/lib/support/string_posix.c',
         'src/core/lib/support/string_util_win32.c',