[perl #43425] local $[: fix scoping during parser error handling.

 Change 22306# inadvertently made 'local $[' statement-scoped
 rather than block-scoped; so revert that change and add a
 different fix. The problem was to ensure that the savestack got
 popped correctly while popping errored tokens. We how record the
 current value of PL_savestack_ix with each pushed parser state.

p4raw-id: //depot/perl@31615

op.c

@@ -4969,6 +4969,12 @@ void
 Perl_cv_undef(pTHX_ CV *cv)
 {
     dVAR;
+
+    DEBUG_X(PerlIO_printf(Perl_debug_log,
+	  "CV undef: cv=0x%"UVxf" comppad=0x%"UVxf"\n",
+	    PTR2UV(cv), PTR2UV(PL_comppad))
+    );
+
 #ifdef USE_ITHREADS
     if (CvFILE(cv) && !CvISXSUB(cv)) {
 	/* for XSUBs CvFILE point directly to static memory; __FILE__ */

pad.c

@@ -255,8 +255,8 @@ Perl_pad_undef(pTHX_ CV* cv)
 	return;
 
     DEBUG_X(PerlIO_printf(Perl_debug_log,
-	  "Pad undef: cv=0x%"UVxf" padlist=0x%"UVxf"\n",
-	    PTR2UV(cv), PTR2UV(padlist))
+	  "Pad undef: cv=0x%"UVxf" padlist=0x%"UVxf" comppad=0x%"UVxf"\n",
+	    PTR2UV(cv), PTR2UV(padlist), PTR2UV(PL_comppad))
     );
 
     /* detach any '&' anon children in the pad; if afterwards they

parser.h

@@ -17,6 +17,7 @@ typedef struct {
     AV	    *comppad; /* value of PL_comppad when this value was created */
 #ifdef DEBUGGING
     const char  *name; /* token/rule name for -Dpv */
+    I32     savestack_ix;	/* size of savestack at this state */
 #endif
 } yy_stack_frame;