- Alternate semantics for Clight where function parameters are temporaries,
  not variables
- New pass SimplLocals that turns non-addressed local variables into
  temporaries
- Simplified Csharpminor, Cshmgen and Cminorgen accordingly
- SimplExpr starts its temporaries above variable names, therefoe
  Cminorgen no longer needs to encode variable names and temps names.
- Simplified Cminor parser & printer, as well as Errors, accordingly.
- New tool clightgen to produce Clight AST in Coq-parsable .v files.
- Removed side condition "return type is void" on rules skip_seq
  in the semantics of CompCert C, Clight, C#minor, Cminor.
- Adapted RTLgenproof accordingly (now uses a memory extension).


git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@2083 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e