Robovm app crashes if gc triggered and there are >=256 threads

[guillerodriguez]

Issue details

If the garbage collector kicks in and there are >= 256 threads alive, the application will crash.

This is due to the following check in bwdgc:

if (GC_mach_threads_count == GC_MAX_MACH_THREADS) // 256
    ABORT("Too many threads");

This is a problem for two reasons:

• Cannot be easily handled by application code
• Behaviour is not obvious: an application can start >= 256 threads and that will not be a problem if the gc does not run

To avoid this I suggest that a check is added in Thread.start() and a RuntimeException is thrown (or perhaps a VirtualMachineError?) if that will exceed the 256 thread limit (note that this includes native threads).

This way at least the application will have a chance to capture the exception and perhaps do something useful with it.