Target of merging with the fix to the semantics of Rawasm

Stack-Aware CompCert with Inlining and Tailcall working properly

Added a flag to generating machine code

Remove CertiKOS-specific features

This is in anticipation of merging with composable-compcert: we keep the
parametrization of each pass over initial states, and the possibility of
empty program definitions, but throw away the parametrized memory model
and some other aspects of CompCertX for CertiKOS.

Update documentation index for release 3.1

Update Changelog for release 2.7.1

For the release, turn off -warn-error

Release builds should not have -warn-error so that they are resilient to addition of new warnings in newer versions of OCaml.

The return type of __builtin_clz() et al is "int", as documented and …

…for GCC compatibility, and not "unsigned int", as previously implemented.

Update the years.