[bazel][build_flags] //build/config:thread_safety_annotations

Port //build/config:thread_safety_annotations to a Bazel
build_flags() target, using THREAD_SAFETY_CFLAGS and
THREAD_SAFETY_DEFINES from
@fuchsia_rules_common//build_flags:default_flag_values.bzl.

Bug: 565437401
Change-Id: I48e120444ab6178b328826b460143a596a6a6964
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1903059
Presubmit-Verified: fuchsia-internal-scoped@luci-project-accounts.iam.gserviceaccount.com <fuchsia-internal-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: David Fang <fangism@google.com>
Fuchsia-Auto-Submit: David Turner <digit@google.com>
Commit-Queue: David Turner <digit@google.com>