Jit: Startup/Shutdown cleanup

A legacy of early parallel Jit development was separate Startup & Shutdown
code for the interpreter half of the jit (dvmJitStartup/dvmJitShutdown)
and the compiler half (dvmCompilerStartup/dvmCompilerShutdown).  This cl
eliminates the dvmJit pair.  Additionally, guard coded added to the
framework callback to return immediately if the Jit isn't active.
5 files changed