[patch][trivial] Fix signed integer overflow in cp-demangle.c (d_number)

[Paul Pluzhnikov via gcc-patches]

Greetings,

This is rather on the trivial side. Google fuzzer found signed integer
overflow in d_number, given this input: _ZZccDF2147483647
Google ref: b141647507.

Ok for trunk?

Thanks,

libiberty/ChangeLog

2019-10-28 Paul Pluzhnikov  <ppluzhni...@google.com>

        * cp-demangle (d_number): Avoid signed int overflow.


--
Paul Pluzhnikov

Index: libiberty/cp-demangle.c
===================================================================
--- libiberty/cp-demangle.c     (revision 277545)
+++ libiberty/cp-demangle.c     (working copy)
@@ -1717,7 +1717,7 @@
        }
       if (ret > ((INT_MAX - (peek - '0')) / 10))
         return -1;
-      ret = ret * 10 + peek - '0';
+      ret = ret * 10 + (peek - '0');
       d_advance (di, 1);
       peek = d_peek_char (di);
     }