cpu.x86.64: define jit-load-vm as a no-op

This was the signal handler prolog code can be shared completely between x86.32 and x86.64.

basis/cpu/x86/64/bootstrap.factor

@@ -38,6 +38,11 @@ IN: bootstrap.x86
     0 JMP f rc-relative rel-word-pic-tail
 ] jit-word-jump jit-define
 
+: jit-load-vm ( -- )
+    ! no-op on x86-64. in factor contexts vm-reg always contains the
+    ! vm pointer.
+    ;
+
 : jit-load-context ( -- )
     ctx-reg vm-reg vm-context-offset [+] MOV ;
 

basis/cpu/x86/bootstrap.factor

@@ -104,9 +104,7 @@ big-endian off
 
     PUSHF
 
-    ! on x86-32 we need to load the vm register
-    ! on x86-64 it's already loaded whenever we're in a factor context
-    bootstrap-cell 4 = [ jit-load-vm ] when ;
+    jit-load-vm ;
 
 : jit-signal-handler-epilog ( -- )
     POPF