RFR(S) 8211743: [AOT] crash in ScopeDesc::decode_body() when JVMTI walks AOT frames

[dean.long at oracle.com]

https://bugs.openjdk.java.net/browse/JDK-8211743
http://cr.openjdk.java.net/~dlong/8211743/webrev/

The fix for JDK-8209574 was a little too aggressive.  We can't turn off 
UseAOT after JVM startup if there is AOT code already loaded, unless we 
deoptimize that code first.  This fix is a redo of that fix, but only 
applied for breakpoints (and not hotswap) and only during startup.

dl