* bignum.c (rb_ll2big): Don't overflow on signed integer negation.

* ext/bigdecimal/bigdecimal.c (MUL_OVERFLOW_SIGNED_VALUE_P): New
  macro.
  (AddExponent): Don't overflow on signed integer multiplication.
  (VpCtoV): Don't overflow on signed integer arithmetic.
  (VpCtoV): Don't overflow on signed integer arithmetic.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@40214 b2dd03c8-39d4-4d8f-98ff-823fe69b080e