Request for reviews (S): 7085137: -XX:+VerifyOops is broken

[Vladimir Kozlov]

http://cr.openjdk.java.net/~kvn/7085137/webrev

7085137: -XX:+VerifyOops is broken

I hit my new assert about different code emit size (7063629) when I specified 
-XX:+VerifyOops on sparc.  It uses set((intptr_t)msg, O0) instruction to set 
address of message which is new each time, as result set() size could be different.
Replace set() with patchable_set() to generate 8 instructions always.
Add missing case Op_PrefetchAllocation in verification code in emit_form3_mem_reg().

Thanks,
Vladimir