intern arbitrary constants

(Best-ability ChangeLog annotation added by Christine Lemmer-Webber.)

* libguile/loader.c (load_thunk_from_memory): Refactor, adding
  "constants" argument and passing to "init" if appropriate.
  (load_thunk_from_file): Call "load-thunk-from-memory" with
  "constants" set to #f.
  (scm_load_thunk_from_memory): Instead of a bytevector, accept
  a cons of "(bytevector . constants)", where constants is either
  a vector or #f.  Pass this into "load_thunk_from_memory".
* module/language/bytecode/spec.scm: Adapt printer.
* module/language/cps/compile-bytecode.scm (compile-bytecode):
  New variable.
* module/system/repl/command.scm (disassemble):
  Adapt to expect pair which includes bytevector as its car.
* module/system/vm/assembler.scm <asm>: Add "to-file?" slot.
  (fresh-block): New variable.
  (make-assembler): Adapt to expect "to-file?" keyword argument.
  (intern-constant): Support "asm-to-file?" in checks.
  (emit-init-constants, link-data): Likewise.
  (link-assembly): Update logic for handling "(bytevector . constants)"
  pair, as well as the expectations of its invocation by compile-bytecode.

module/language/bytecode/spec.scm

@@ -37,6 +37,7 @@
 (define-language bytecode
   #:title	"Bytecode"
   #:compilers   `((value . ,bytecode->value))
-  #:printer	(lambda (bytecode port) (put-bytevector port bytecode))
+  #:printer	(lambda (x port)
+                  (put-bytevector port (car x)))
   #:reader      get-bytevector-all
   #:for-humans? #f)