x86: Fix disassemble annotation of negative offsets.

FDEFNs can now end up being located at negative signed word locations.

src/compiler/x86/target-insts.lisp

@@ -213,13 +213,13 @@
  (when (and offset (or firstp (not (zerop offset))))
  (unless (or firstp (minusp offset))
  (write-char #\+ stream))
- (if firstp
- (progn
- (princ16 offset stream)
- (or (minusp offset)
- (nth-value 1 (note-code-constant-absolute offset dstate))
-  (maybe-note-assembler-routine offset nil dstate)))
- (princ offset stream))))))
+ (cond (firstp
+  (princ16 offset stream)
+  (let ((offset (ldb (byte 32 0) offset)))
+  (or (nth-value 1 (note-code-constant-absolute offset dstate))
+  (maybe-note-assembler-routine offset nil dstate))))
+ (t
+  (princ offset stream)))))))
  (write-char #\] stream))
 
 ;;;; interrupt instructions