x86-64: Actually fix an already-removed FIXME

Strangely rev 9e244505ab deleted a remark about fixing reliance on a
do-nothing vop without solving it. Do that now by guarding an unreachable
use of a VOP macro in EMIT-INITS based on +/-executable-funinstances.

src/assembly/x86-64/tramps.lisp

@@ -228,13 +228,6 @@
   (loadw rax-tn rax-tn fdefn-fun-slot other-pointer-lowtag)
   (inst jmp (object-slot-ea rax-tn closure-fun-slot fun-pointer-lowtag)))
 
-#-compact-instance-header
-(define-assembly-routine
-    (funcallable-instance-tramp (:return-style :none))
-    ()
-  (loadw rax-tn rax-tn funcallable-instance-function-slot fun-pointer-lowtag)
-  (inst jmp (object-slot-ea rax-tn closure-fun-slot fun-pointer-lowtag)))
-
 (define-assembly-routine (ensure-symbol-hash (:return-style :raw)) ()
   (with-registers-preserved (lisp)
     (inst mov rdx-tn (ea 16 rbp-tn)) ; arg

src/compiler/generic/vm-ir2tran.lisp

@@ -77,6 +77,7 @@
   (let ((unbound-marker-tn nil)
         (funcallable-instance-tramp-tn nil)
         (dx-p (node-stack-allocate-p node)))
+    (declare (ignorable funcallable-instance-tramp-tn))
     (flet ((zero-init-p (x)
              ;; dynamic-space is already zeroed
              (and (not dx-p)
@@ -137,6 +138,7 @@
                                     tn))))
                        (:null
                         (emit-constant nil))
+                       #-executable-funinstances
                        (:funcallable-instance-tramp
                         (or funcallable-instance-tramp-tn
                             (setf funcallable-instance-tramp-tn

src/compiler/x86-64/alloc.lisp

@@ -1008,15 +1008,6 @@
 
 ;;;; automatic allocators for primitive objects
 
-(define-vop (make-funcallable-instance-tramp)
-  (:args)
-  (:results (result :scs (any-reg)))
-  (:vop-var vop)
-  (:generator 1
-    ;; gets "... is not the name of a defined VOP." if not defined at all
-    #+compact-instance-header (bug "Shouldn't get here")
-    (inst mov result (make-fixup 'funcallable-instance-tramp :assembly-routine))))
-
 (flet
   ((alloc (vop name words type lowtag stack-allocate-p result
                     &optional alloc-temp node

src/compiler/x86-64/target-insts.lisp

@@ -699,8 +699,7 @@
                              operand inst))))
                ((or (eq inst lea-inst)
                     (and (eq inst mov-inst) (eql opcode #x8B)))
-                ;; Computing the address of UNDEFINED-FDEFN and
-                ;; FUNCALLABLE-INSTANCE-TRAMP is done with LEA.
+                ;; Computing the address of UNDEFINED-FDEFN is done with LEA.
                 ;; Load from the alien linkage table can be done with MOV Rnn,[RIP-k].
                 (let ((modrm (sap-ref-8 sap (1+ (dstate-cur-offs dstate)))))
                   (when (= (logand modrm #b11000111) #b00000101) ; RIP-relative mode