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

libsrc/rp6502/crt0.s

@@ -24,9 +24,9 @@ _init:
 
 ; Set cc65 argument stack pointer
     lda #<(__RAM_START__ + __RAM_SIZE__)
-    sta sp
+    sta spc
     lda #>(__RAM_START__ + __RAM_SIZE__)
-    sta sp+1
+    sta spc+1
 
 ; Initialize memory storage
     jsr zerobss   ; Clear BSS segment

libsrc/rp6502/ria.s

@@ -11,7 +11,7 @@
 .export _ria_call_int, _ria_call_long
 .export _ria_call_int_errno, _ria_call_long_errno
 
-.importzp sp, sreg
+.importzp spc, sreg
 .import ___mappederrno, incsp1
 
 .code

libsrc/rp6502/xreg.s

@@ -5,7 +5,7 @@
 ; int __cdecl__ xreg(char device, char channel, unsigned char address, ...);
 
 .export _xreg
-.importzp sp
+.importzp spc
 .import addysp, _ria_call_int_errno
 
 .include "rp6502.inc"
@@ -20,12 +20,12 @@
 
 @copy: ; copy stack
     dey
-    lda (sp),y
+    lda (spc),y
     sta RIA_XSTACK
     tya
     bne @copy
 
-    ; recover variadic size and move sp
+    ; recover variadic size and move spc
     txa
     tay
     jsr addysp