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This reduces the stack space reserved for overflow checks to 12K, split
into an 8K gap and a 4K protected region.  GC needs over 8K when running
in a stack overflow situation.

Also prevents signal runaway by detecting a signal inside code that
resulted from a signal handler invokation.  And adds a max signal count to
the SignalTest to prevent it running forever.

Also reduces the number of iterations for the InterfaceTest as this was
taking (almost) forever with the --trace option on run-test.

Bug: 15435566

Change-Id: Id4fd46f22d52d42a9eb431ca07948673e8fda694

Conflicts:
	compiler/optimizing/code_generator_x86_64.cc
	runtime/arch/x86/fault_handler_x86.cc
	runtime/arch/x86_64/quick_entrypoints_x86_64.S