Split immediate symbol and immediate constant cases.

git-svn-id: http://caml.inria.fr/svn/ocaml/branches/abstract_intel_emit@15284 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
Simplify.

git-svn-id: http://caml.inria.fr/svn/ocaml/branches/abstract_intel_emit@15285 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
Fix.

git-svn-id: http://caml.inria.fr/svn/ocaml/branches/abstract_intel_emit@15286 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
Represent symbol addresses in a uniform way in the AST.  The instruction emitter decides the interpret them as absolute or relative addresses.

git-svn-id: http://caml.inria.fr/svn/ocaml/branches/abstract_intel_emit@15287 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02