instead of our custom .go format, use elf

* libguile/objcodes.c: Change to expect objcode on disk to be embedded
  in ELF instead of having the funky cookie.

  (to_native_order): Use already existing SCM_BYTE_ORDER style byte
  order instead of chars.
  (bytecode_to_objcode): No need for word_size arg.
  (scm_bytecode_to_objcode, scm_objcode_to_bytecode): Take optional
  endianness arg instead of sometimes using target-endianness.
  (scm_load_objcode, scm_write_objcode, scm_bytecode_to_native_objcode):
  Remove.

* libguile/objcodes.h: Adapt.

* libguile/vm.c (scm_load_compiled_with_vm): Use
  scm_load_thunk_from_file.
  (make_boot_program): Adapt to use scm_bytecode_to_objcode with
  endianness arg.

* module/Makefile.am (OBJCODE_LANG_SOURCES): Add (language objcode
  elf).
* module/language/objcode/elf.scm: New module, embeds objcode in ELF.

* module/language/bytecode/spec.scm (compile-objcode):
  (decompile-objcode): Use (target-endianness).

* module/language/objcode/spec.scm: use (language objcode elf) for
  write-objcode.

* module/scripts/disassemble.scm (disassemble):
* module/system/repl/command.scm (disassemble-file): Use
  load-thunk-from-file.

* module/system/vm/objcode.scm: Remove load-objcode and write-objcode.

* test-suite/tests/asm-to-bytecode.test (test-target): Adapt to the new
  ELF world.

test-suite/tests/asm-to-bytecode.test

@@ -22,7 +22,9 @@
   #:use-module (test-suite lib)
   #:use-module (system vm instruction)
   #:use-module (system vm objcode)
+  #:use-module (system vm elf)
   #:use-module (system base target)
+  #:use-module (language objcode elf)
   #:use-module (language assembly)
   #:use-module (language assembly compile-bytecode))
 
@@ -167,20 +169,12 @@
                                      (nop) (nop) (nop)
                                      (nop) (nop))
                       #f)))
-              (write-objcode (bytecode->objcode b) p)
-              (let ((cookie   (make-bytevector %objcode-cookie-size))
-                    (expected (format #f "GOOF----~a-~a"
-                                      (cond ((eq? endian (endianness little))
-                                             "LE")
-                                            ((eq? endian (endianness big))
-                                             "BE")
-                                            (else
-                                             (error "unknown endianness"
-                                                    endian)))
-                                      word-size)))
-                (bytevector-copy! (get-objcode) 0 cookie 0
-                                  %objcode-cookie-size)
-                (string=? (utf8->string cookie) expected)))))))))
+              (write-objcode (bytecode->objcode b (target-endianness)) p)
+              (let* ((bv (get-objcode)))
+                (and=> (parse-elf bv)
+                       (lambda (elf)
+                         (and (equal? (elf-byte-order elf) endian)
+                              (equal? (elf-word-size elf) word-size))))))))))))
 
 (with-test-prefix "cross-compilation"
 
@@ -202,7 +196,7 @@
                                                    (make-int8 77)
                                                    (return))
                                     #f))
-               (o (bytecode->objcode b)))
+               (o (bytecode->objcode b (target-endianness))))
           (with-target "fcpu-unknown-gnu1.0"
             (lambda ()
               (write-objcode o p))))))))