Do l-value conversion, etc., on a switch condition expression in

Do l-value conversion, etc., on a switch condition expression in
ActOnStartOfSwitchStmt (i.e. before binding up a full-expression)
instead of ActOnFinishSwitchStmt.

Among other things, this means that property l-values are properly
converted inside the full-expression.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@137014 91177308-0d34-0410-b5e6-96231b3b80d8