precompute log2(e)

Kind of a freebie.  No interesting change in test case precision.

Change-Id: Ib26ddc5de31f0a456c2c41d92bb457ccdeb12e93
Reviewed-on: https://skia-review.googlesource.com/c/skcms/+/247725
Commit-Queue: Mike Klein <mtklein@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
1 file changed