Provide finer grained control over --smart-indexing.

The --smart-indexing option enables a number of smart indexing strategies
depending on the switch category and backend.  This diff adds new developer
only options that provide finer grained control over which smart indexing
strategies are enabled.  I need this to assist in tracking down some problems
with the use of --smart-indexing on the MinGW64 port.

compiler/options.m:
	Add new command line options that can be used to selectively disable
	various types of smart indexing.

compiler/switch_util.m:
	Add a predicate to test whether the user has chosen to disable smart
	indexing for a particular category of switch.

compiler/switch_gen.m:
compiler/ml_switch_gen.m:
	Respect the new options.