It's the name that's NULL when an array isn't found

And missing prototypes

Untested

Not so much for old machines, as for getting decent performance
when not setting -march= (SSE2 is part of the amd64 ABI).

Should be able to handle all previous GRU variants and more.

Should work for both CBR and VBR. In the CBR case, we can make
CELT VBR and use DRED to fill the rest.