Make sure dcdx/dcdy are stored as 32bit quantities.

Will allow usage of sse multiplies.
llvmpipe: add support for 32bit optimized sse paths

if the triangle is bounded by a 128x128 box then we can
use only 32bit arthemtic which is nice because the sse
paths for it can be nicely optimized.
llvmpipe: fix the int64_t printing warnings

we need to use the standard defines from inttypes.h in order
to consistently avoid the compile warnings.
llvmpipe: enable 32 bit sse paths in the triangle setup

we can use the 32 bit sse paths if the fb is smaller than
the largest bounding box is known to not cause an overflow
and triangle fits within the box.