Add SkLog implementation to SkSLMinify

https://review.skia.org/1247176 changes SK_ABORT to invoke SKIA_LOG which expands into SkLog, while SK_ABORT used to expand into SkDebugf. This tool would define a custom implementation of SkDebugf, now it needs to define SkLog for itself.

Change-Id: I21bbedf8635f237d6b27b0f333c5b5dab88c2a7b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/1247397
Auto-Submit: Jorge Betancourt <jmbetancourt@google.com>
Reviewed-by: Florin Malita <fmalita@google.com>
Commit-Queue: Florin Malita <fmalita@google.com>