Correctly copy inner exception structs when building for ARM. (#166)

Fixes #164.

unwind-arm.h

@@ -203,7 +203,7 @@ _Unwind_Reason_Code name(_Unwind_State state,\
 #define CALL_PERSONALITY_FUNCTION(name) name(state,exceptionObject,context)
 
 #define COPY_EXCEPTION(dst, src) \
-  memcpy((dst)->unwinder_cache, (src)->unwinder_cache, sizeof(struct unwinder_cache)); \
-  memcpy((dst)->barrier_cache, (src)->barrier_cache, sizeof(struct barrier_cache)); \
-  memcpy((dst)->cleanup_cache, (src)->cleanup_cache, sizeof(struct cleanup_cache)); \
-  memcpy((dst)->pr_cache, (src)->pr_cache, sizeof(struct pr_cache));
+  (dst)->unwinder_cache = (src)->unwinder_cache; \
+  (dst)->barrier_cache = (src)->barrier_cache; \
+  (dst)->cleanup_cache = (src)->cleanup_cache; \
+  (dst)->pr_cache = (src)->pr_cache;