rename "sp" to "spc", avoid conflict with 4510 opcodes

libsrc/cbm/dir.s

@@ -44,10 +44,10 @@ __dirread:
 ; Replace dir by dir->fd
 
         ldy     #2
-        lda     (sp),y
+        lda     (spc),y
         sta     ptr1
         iny
-        lda     (sp),y
+        lda     (spc),y
         sta     ptr1+1
         ldy     #DIR::fd+1
         lda     (ptr1),y
@@ -55,10 +55,10 @@ __dirread:
         dey
         lda     (ptr1),y
         ldy     #2
-        sta     (sp),y
+        sta     (spc),y
         pla
         iny
-        sta     (sp),y
+        sta     (spc),y
 
 ; Get count, save it again, clear the high byte and call read(). By the
 ; previous actions, the stack frame is as read() needs it, and read() will

libsrc/cbm/open.s

@@ -12,7 +12,7 @@
         .import         opencmdchannel, closecmdchannel, readdiskerror
         .import         fnunit, fnisfile
         .import         _close
-        .importzp       sp, tmp2, tmp3
+        .importzp       spc, tmp2, tmp3
 
         .include        "errno.inc"
         .include        "fcntl.inc"

libsrc/cbm/write.s

@@ -8,7 +8,7 @@
         .constructor    initstdout
 
         .import         rwcommon
-        .importzp       sp, ptr1, ptr2, ptr3
+        .importzp       spc, ptr1, ptr2, ptr3
 
         .include        "cbm.inc"
         .include        "errno.inc"