isl_hash_dim: make result independent of endianness

isl_hash_dim: make result independent of endianness

The result computed by isl_hash_dim may affect the order of maps
in a union map, which may in turn affect the result of AST generation.
In particular, we would generate slightly different output depending
on endianness, causing the tests to fail on big endian machines since
the generated output is compared to output generated on a little endian
machine.

Instead of hashing in the dimensions of the space as integers,
we now only hash in the least significant byte.
This has some effect on the results of AST generation, but the output
should now be the same on little endian and big endian.

Reported-by: Richard Biener <rguenther@suse.de>
Signed-off-by: Sven Verdoolaege <skimo@kotnet.org>