fix leak with local ${^WARNING_BITS} = ...

When restoring the old value, need to free the current value first.
Can be reproduced with

    {
        local ${^WARNING_BITS} = 'swit';
    }

when run under ASan or similar.
An equivalent test already exists in t/op/leaky-magic.t.

1 files changed, 2 insertions, 0 deletions

diff --git a/mg.c b/mg.c
index b022d63442..320e2d39bb 100644
--- a/mg.c
+++ b/mg.c
@@ -2916,6 +2916,8 @@ Perl_magic_set(pTHX_ SV *sv, MAGIC *mg)
 	else if (strEQ(mg->mg_ptr+1, "ARNING_BITS")) {
 	    if ( ! (PL_dowarn & G_WARN_ALL_MASK)) {
 		if (!SvPOK(sv)) {
+                    if (!specialWARN(PL_compiling.cop_warnings))
+                        PerlMemShared_free(PL_compiling.cop_warnings);
 	            PL_compiling.cop_warnings = pWARN_STD;
 		    break;
 		}