[wide-int] Add fast path for hosts with HWI widening multiplication

[Richard Sandiford]

Ian Lance Taylor <iant@google.com> writes:
> On Sun, Dec 1, 2013 at 2:28 AM, Richard Sandiford
> <rdsandiford@googlemail.com> wrote:
>> I followed Joseph's suggestion and reused longlong.h.  I copied it from
>> libgcc rather than glibc since it seemed better for GCC to have a single
>> version across both gcc/ and libgcc/.  I can put it in include/ if that
>> seems better.
>
> Actually copying complex code like this does not seem maintainable.  I
> think there needs to be only one copy in the GCC sources.  If that
> requires moving it back from libgcc to gcc, or moving it to include,
> do that.

OK, will do, but which do you prefer?

Thanks,
Richard