Disable SkFontMgr::RefDefault() for Bazel buffet build

Along the way, I realized some of the tests fail on M1 Macs,
due to "-ffp-contract=on" being on by default and actually making
a difference in some unit tests. This adds some asserts/debugging
code that helped along the way.

Change-Id: I213f8d8967bd9ec0da2de635390a42dff4e9faaa
Bug: b/305780908
Bug: b/40045064
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/768079
Commit-Queue: Kevin Lubick <kjlubick@google.com>
Reviewed-by: Ben Wagner <bungeman@google.com>
Reviewed-by: Leandro Lovisolo <lovisolo@google.com>
10 files changed