compiler-context-analysis: Introduce header suppressions

While we can opt in individual subsystems which add the required
annotations, such subsystems inevitably include headers from other
subsystems which may not yet have the right annotations, which then
result in false positive warnings.

Making compatible by adding annotations across all common headers
currently requires an excessive number of __no_context_analysis
annotations, or carefully analyzing non-trivial cases to add the correct
annotations. While this is desirable long-term, providing an incremental
path causes less churn and headaches for maintainers not yet interested
in dealing with such warnings.

Rather than clutter headers unnecessary and mandate all subsystem
maintainers to keep their headers working with context analysis,
suppress all -Wthread-safety warnings in headers. Explicitly opt in
headers with context-enabled primitives.

With this in place, we can start enabling the analysis on more complex
subsystems in subsequent changes.

Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20251219154418.3592607-26-elver@google.com