swift234

This patch makes it easier for the debugger to
insert the values for variables into the SIL for
expressions correctly. 

Instead of hijacking emitLValueForDecl() in
SILGenFunction, we now hook into
emitInitializationForVarDecl.  That way we can
emit the proper value and just stick it into
VarLocs.

To support this, we also make two other changes:

- We suppress marking the variable uninitialized
  in MarkPatternUninitialized::visitNamedPattern.

- We override DeclChecker in the type checker to
  allow LLDB to construct let statements without
  initializers.


Swift SVN r18676