Define I64 before I32 for better encoding table compression.
Define I64 before I32 for better encoding table compression.

The encoding list compression algorithm is not the sharpest knife in the
drawer. It can reuse subsets of I64 encoding lists for I32 instructions,
but only when the I64 lists are defined first.

With this change and the previous change to the encoding list format, we
get the following table sizes for the Intel ISA:

ENCLISTS: 1478 B ->  662 B
LEVEL2:             1072 B (unchanged)
LEVEL1:     32 B ->   48 B
Total:    2582 B -> 1782 B (-31%)

sunfishcode/cretonne,stoklund/cretonne,stoklund/cretonne,sunfishcode/cretonne,stoklund/cretonne,sunfishcode/cretonne