Clone R-O inversion list before modifying it

Unicode-defined properties are kept in inversion lists in read-only
memory.  Attempting to modify them will result in a segfault.  The new
Unicode 16.0 has some empty properties that need to be inverted before
use in some cases.  This situation has not occurred before.  The
inversion code that gets called presumes it has a modifiable SV and
inverts in-place.  This segfaults.

Normally, no inversion is needed, and the properties are used as-is, and
no problem arises.

The solution here is to create a clone, and then invert that.

Author: khwilliamson

regcomp.c

@@ -14764,6 +14764,14 @@ S_parse_uniprop_string(pTHX_
     /* Here, we are either done with the whole property name, if it was simple;
      * or are positioned just after the '=' if it is compound. */
 
+    /* When we get a system inversion list, it is a global that needs to be
+     * preserved for later, and not coincidentally is in read-only memory.
+     * So we set this boolean to true once we've made a copy, and then we are
+     * free to modify the copy.  It has to be set here way above where it is
+     * needed, in order to not run afoul of the C++ compiler saying goto's
+     * cross its initialization */
+    bool cloned = false;
+
     if (equals_pos >= 0) {
         assert(stricter == Not_Strict); /* We shouldn't have set this yet */
 
@@ -15916,12 +15924,16 @@ S_parse_uniprop_string(pTHX_
                 _invlist_union(prop_definition, pu_invlist,
                                &expanded_prop_definition);
                 prop_definition = expanded_prop_definition;
+                cloned = true;
                 Perl_ck_warner_d(aTHX_ packWARN(WARN_EXPERIMENTAL__PRIVATE_USE), "The private_use feature is experimental");
             }
         }
     }
 
     if (invert_return) {
+        if (! cloned) {
+           prop_definition = sv_2mortal(invlist_clone(prop_definition, NULL));
+        }
         _invlist_invert(prop_definition);
     }
     return prop_definition;