[OG10][committed] amdgcn: Allow V64DFmode min/max reductions

[Andrew Stubbs]

Now backported to devel/omp/gcc-10.

On 26/01/2021 10:29, Andrew Stubbs wrote:

This patch fixes and AMD GCN bug in which attempting to use DFmode vector reductions would cause an ICE.

There's no reason not to allow the reductions, so we simply enable them thusly.

Andrew