gallivm: allow large numbers of temporaries

gallivm: allow large numbers of temporaries

The number of allowed temporaries increases almost with every
iteration of an api. We used to support 128, then we started
increasing and the newer api's support 4096+. So if we notice
that the number of temporaries is larger than our statically
allocated storage would allow we just treat them as indexable
temporaries and allocate them as an array from the start.

Signed-off-by: Zack Rusin <zackr@vmware.com>
Reviewed-by: Jose Fonseca <jfonseca@vmware.com>
Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Roland Scheidegger <sroland@vmware.com>