OSX: Use __thread attribute.

src/lj_err.c

@@ -290,12 +290,7 @@ LJ_FUNCA int lj_err_unwind_dwarf(int version, int actions,
 }
 
 #if LJ_UNWIND_EXT
-#if LJ_TARGET_OSX || defined(__OpenBSD__)
-/* Sorry, no thread safety for OSX. Complain to Apple, not me. */
-static _Unwind_Exception static_uex;
-#else
 static __thread _Unwind_Exception static_uex;
-#endif
 
 /* Raise DWARF2 exception. */
 static void err_raise_ext(int errcode)