swift234

Implement SILInstruction::isIdenticalTo for all literal types in preparation for CSE.

The code here is a simple checklist. It performs the following checks in order:

1. Quick check to see if the kind/number of operands/number of types match up.
2. Comparison all of the types/operands.
3. Finally use a switch to perform specialized per instruction comparisons on
state not represented in the instructions types/operands (i.e. vardecls,
structdecls, etc.).

Additionally the switch is setup so that instructions which have not been fully
implemented in the switch will cause an unreachable to be hit. Once all
instructions have isIdenticalTo implementations (implying the switch is
covered), I will remove the unreachable.

*NOTE* The primary use case for this now is CSE. In CSE we can control which
instructions we process so during the review process I am only going to process
literals for the sake of simplicity (and thus this patch contains only code for
checking literals).

Swift SVN r10743