[clang] [llvm] [Sanitizers] Support sanitizer instrumentation regions in KMSAN, KASAN, KCOV and KCSAN (PR #231374)

[Marco Elver via cfe-commits]

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@@ -91,6 +91,39 @@ positives and therefore should be used with care, and only if absolutely
 required; for example for certain code that cannot tolerate any instrumentation
 and resulting side-effects. This attribute overrides `no_sanitize("memory")`.
 
+### Re-enabling Instrumentation in Regions
+
+In KernelMemorySanitizer (KMSAN), a function with
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melver wrote:

I think the feature will be less niche if it's also allowed for user space (mode-independent) MSan. The builtins are new, so accidental use is unlikely.

https://github.com/llvm/llvm-project/pull/231374