Fix __builtin_{smulll,saddll}_overflow() usage
Fix __builtin_{smulll,saddll}_overflow() usage

- Use a variable of type long long variable not int64_t as they may be
  different sizes.

- Fixes "warning: incompatible pointer types passing 'int64_t *' (aka 'long *')
  to parameter of type 'long long *' [-Wincompatible-pointer-types]"

e78l/swift-corelibs-foundation,apple/swift-corelibs-foundation,e78l/swift-corelibs-foundation,e78l/swift-corelibs-foundation,apple/swift-corelibs-foundation,apple/swift-corelibs-foundation,e78l/swift-corelibs-foundation,apple/swift-corelibs-foundation,e78l/swift-corelibs-foundation,apple/swift-corelibs-foundation