nmethod::make_not_entrant() and native methods

[Andrew Haley]

On AArch64 we have to place a NOP at the start of every compiled
method so that we can, if needs be, patch its verified entry point.
This is because of an architectural restriction that only nops, traps,
and branches may be patched while code is running.

I am guessing that we do not need a NOP at the start of a compiled
native wrapper because it will never be deoptimized.  Is that right?

Thanks,
Andrew.