Add desugaring.{cpp,h} to BUILD.
Add desugaring.{cpp,h} to BUILD.

Related to #3

lamuguo/jsonnet,jbeda/jsonnet,Neeke/jsonnet,davidzchen/jsonnet,huggsboson/jsonnet,sparkprime/jsonnet,huggsboson/jsonnet,davidzchen/jsonnet,jbeda/jsonnet,davidzchen/jsonnet,Neeke/jsonnet,google/jsonnet,sparkprime/jsonnet,lamuguo/jsonnet,lamuguo/jsonnet,huggsboson/jsonnet,google/jsonnet,Neeke/jsonnet,lamuguo/jsonnet,google/jsonnet,google/jsonnet,davidzchen/jsonnet,sparkprime/jsonnet,sparkprime/jsonnet,jbeda/jsonnet,huggsboson/jsonnet,davidzchen/jsonnet,jbeda/jsonnet,google/jsonnet,lamuguo/jsonnet,huggsboson/jsonnet,google/jsonnet,sparkprime/jsonnet,jbeda/jsonnet,Neeke/jsonnet,sparkprime/jsonnet,Neeke/jsonnet