libiberty d_compact_number signed integer overflow

https://lists.gnu.org/archive/html/bug-binutils/2026-06/msg00189.html
Fix this by doing the addition in unsigned arithmetic.

Applying to binutils and gcc as obvious.

diff --git a/libiberty/cp-demangle.c b/libiberty/cp-demangle.c
index 5f08ef8946a..ab122fc388d 100644
--- a/libiberty/cp-demangle.c
+++ b/libiberty/cp-demangle.c
@@ -3266,7 +3266,7 @@ d_compact_number (struct d_info *di)
   else if (d_peek_char (di) == 'n')
     return -1;
   else
-    num = d_number (di) + 1;
+    num = d_number (di) + 1u;
 
   if (num < 0 || ! d_check_char (di, '_'))
     return -1;

-- 
Alan Modra