Add library function for null pointer checking.

This is used by the new ORCA/C debugging option to check for illegal use of null pointers. It is similar to an existing routine in PasLib used by ORCA/Pascal's similar checks.

cc.asm

@@ -433,6 +433,24 @@ ret      tya                            store return value in result space
          rtl                            return to original caller
          end
 
+****************************************************************
+*
+*  ~CheckPtrC - check a pointer to insure it is not null
+*
+*  Inputs:
+*       1,S - return address
+*       4,S - pointer
+*
+****************************************************************
+*
+~CheckPtrC start
+        lda   4,S
+        ora   5,S
+        bne   lb1
+        error #1                        subrange exceeded
+lb1     rtl
+        end
+
 ****************************************************************
 *
 *  ~CUMul2 - unsigned multiply