compiler-capability-analysis: Add infrastructure for Clang's capability analysis

Capability analysis is a C language extension, which enables statically
checking that user-definable "capabilities" are acquired and released where
required. An obvious application is lock-safety checking for the kernel's
various synchronization primitives (each of which represents a "capability"),
and checking that locking rules are not violated.

Clang originally called the feature "Thread Safety Analysis" [1], with
some terminology still using the thread-safety-analysis-only names. This
was later changed and the feature became more flexible, gaining the
ability to define custom "capabilities". Its foundations can be found in
"capability systems", used to specify the permissibility of operations
to depend on some capability being held (or not held).

[1] https://clang.llvm.org/docs/ThreadSafetyAnalysis.html
[2] https://www.cs.cornell.edu/talc/papers/capabilities.pdf

Because the feature is not just able to express capabilities related to
synchronization primitives, the naming chosen for the kernel departs
from Clang's initial "Thread Safety" nomenclature and refers to the
feature as "Capability Analysis" to avoid confusion. The implementation
still makes references to the older terminology in some places, such as
`-Wthread-safety` being the warning enabled option that also still
appears in diagnostic messages.

See more details in the kernel-doc documentation added in this and the
subsequent changes.

A Clang version that supports -Wthread-safety-addressof is recommended,
but not required: llvm/llvm-project#123063

Signed-off-by: Marco Elver <[email protected]>

Author: melver

Makefile

@@ -1082,6 +1082,7 @@ include-$(CONFIG_KCOV)		+= scripts/Makefile.kcov
 include-$(CONFIG_RANDSTRUCT)	+= scripts/Makefile.randstruct
 include-$(CONFIG_AUTOFDO_CLANG)	+= scripts/Makefile.autofdo
 include-$(CONFIG_PROPELLER_CLANG)	+= scripts/Makefile.propeller
+include-$(CONFIG_WARN_CAPABILITY_ANALYSIS) += scripts/Makefile.capability-analysis
 include-$(CONFIG_GCC_PLUGINS)	+= scripts/Makefile.gcc-plugins
 
 include $(addprefix $(srctree)/, $(include-y))