PR82809: register handling in ix86_vector_duplicate_value

[Uros Bizjak]

> 2017-11-02  Richard Sandiford  <richard.sandiford@linaro.org>
>
> gcc/
> PR target/82809
> * config/i386/i386.c (ix86_vector_duplicate_value): Use
> gen_vec_duplicate after forcing the scalar into a register.
>
> gcc/testsuite/
> * gcc.dg/pr82809.c: New test.

OK.

Thanks,
Uros.