Don't use IMMEDIATE in icore

Since the fix of its RAM addr, we use the wrong CURRENT in every
usage of IMMEDIATE in icore. We therefore have to manually set the
flag for all 3 immediate words in that unit.

forth/icore.fs

@@ -53,7 +53,11 @@
     '           ( get word )
     -^          ( apply offset )
     ,           ( write! )
-; IMMEDIATE
+;
+( We can't use IMMEDIATE because the one we've just compiled
+  in z80c target's the *target*'s RAM addr, not the host's.
+  manually set namelen field. )
+0x82 CURRENT @ 1 - C!
 
 : RAM+
     [ RAMSTART LITN ] _c +
@@ -219,7 +223,10 @@
 
 ( : and ; have to be defined last because it can't be
   executed now also, they can't have their real name
-  right away )
+  right away. We also can't use IMMEDIATE because the offset
+  used for CURRENT is the *target*'s RAM offset. we're still
+  on the host.
+)
 
 : X
     _c (entry)
@@ -235,15 +242,17 @@
     ( maybe number )
     ELSE _c (parse*) _c @ EXECUTE _c LITN THEN
     AGAIN
-; IMMEDIATE
+;
 
 : Y
     ['] EXIT _c ,
     _c R> _c DROP     ( exit : )
-; IMMEDIATE
+;
 
-( Give ":" and ";" their real name )
+( Give ":" and ";" their real name and make them IMMEDIATE )
+0x81 ' X 1 - C!
 ':' ' X 4 - C!
+0x81 ' Y 1 - C!
 ';' ' Y 4 - C!
 
 ( Add dummy entry. we use CREATE because (entry) is, at this