finit-local-zero and default initialization

[Asher Langton]

I'm planning to add support for -finit-local-zero (PR20441), as well
as for arbitrary default initializations specified at compile-time.
One request from within LLNL has been for a way to control the default
initialization values at runtime, via some simple library routines
(set_default_integer, get_default_integer, etc.).  This would be very
useful for debugging large codes without recompiling an entire
project.  Any comments, suggestions, or objections?

Thanks,
Asher