[gcc r17-3389] fortran: [PR126816] Fix use-after-free of charlen from rejected trial

https://gcc.gnu.org/g:0a59650d1ec84d0e155670ef5ae226e4c59ba748

commit r17-3389-g0a59650d1ec84d0e155670ef5ae226e4c59ba748
Author: Jerry DeLisle <[email protected]>
Date:   Tue Aug 18 09:46:21 2026 -0700

    fortran: [PR126816] Fix use-after-free of charlen from rejected trial
    
    restore_old_symbol reverted only ts.type/ts.kind when undoing a
    tentative symbol change, leaving ts.u.cl pointing at whatever
    charlen the rejected trial had allocated via gfc_set_default_type.
    Restore the whole typespec instead.
    
            PR fortran/126816
    
    gcc/fortran/ChangeLog:
    
            * symbol.cc (restore_old_symbol): Restore the whole typespec
            instead of just type and kind.

Diff:
---
 gcc/fortran/symbol.cc | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/gcc/fortran/symbol.cc b/gcc/fortran/symbol.cc
index dde3e92a33d3..57e3daa5767a 100644
--- a/gcc/fortran/symbol.cc
+++ b/gcc/fortran/symbol.cc
@@ -3817,8 +3817,9 @@ restore_old_symbol (gfc_symbol *p)
   p->mark = 0;
   old = p->old_symbol;
 
-  p->ts.type = old->ts.type;
-  p->ts.kind = old->ts.kind;
+  /* Restore the whole typespec, not just type/kind, so ts.u.cl doesn't
+     dangle.  */
+  p->ts = old->ts;
 
   p->attr = old->attr;