fixup! [op.c] Break fragile long-distance dependency on keyword list order

Author: Branislav Zahradník

op.c

@@ -16172,7 +16172,7 @@ Perl_coresub_op(pTHX_ SV * const coreargssv, const int code,
 
     switch(opnum) {
     case 0: {
-        int caller_index = -1;
+        IV caller_index = -1;
         switch (-code) {
             case KEY___PACKAGE__: caller_index = 0; break; /* (caller)[0] */
             case KEY___FILE__:    caller_index = 1; break; /* (caller)[1] */