compilation passes return third value: the continuation environment

* module/system/base/compile.scm: Expect compile passes to produce three
  values, not two. The third is the "continuation environment", the
  environment that can be used to compile a subsequent expression from
  the same source language. For example, expansion-time side effects can
  set the current module, which would be reflected appropriately in the
  continuation environment.

* module/language/assembly/compile-bytecode.scm:
* module/language/bytecode/spec.scm:
* module/language/ecmascript/compile-ghil.scm:
* module/language/ghil/compile-glil.scm:
* module/language/glil/spec.scm:
* module/language/objcode/spec.scm:
* module/language/scheme/compile-ghil.scm:
* module/system/base/compile.scm: Update compile passes to return a
  continuation environment.

module/language/ghil/compile-glil.scm

@@ -29,7 +29,8 @@
 (define (compile-glil x e opts)
   (if (memq #:O opts) (set! x (optimize x)))
   (values (codegen x)
-          (and e (cons (car e) (cddr e)))))
+          (and e (cons (car e) (cddr e)))
+          e))
 
 
 ;;;