[clang] [rtsan][NFC] Documentation of suppression flag (PR #112727)

[Chris Apple via cfe-commits]

================
@@ -194,12 +198,43 @@ Some issues with flags can be debugged using the ``verbosity=$NUM`` flag:
    misspelled_flag
    ...
 
-Disabling
----------
+Disabling and suppressing
+-------------------------
 
-In some circumstances, you may want to suppress error reporting in a specific scope.
+There are multiple ways to suppress error reporting when using RealtimeSanitizer.
 
-In C++, this is achieved via  ``__rtsan::ScopedDisabler``. Within the scope where the ``ScopedDisabler`` object is instantiated, all sanitizer error reports are suppressed. This suppression applies to the current scope as well as all invoked functions, including any functions called transitively.
+In general, ``ScopedDisabler`` should be preferred, as it is the most performant.
+
+.. list-table:: Suppression methods
+   :widths: 30 15 15 10 70
+   :header-rows: 1
+
+   * - Suppression method
+     - Specified at?
+     - Scope
+     - Run-time cost
+     - Description
+   * - ``ScopedDisabler``
+     - Compile-time
+     - Stack
+     - Very low
----------------
cjappl wrote:

Yeah, I think it's good that you raised it, especially because I had the exact same back and forth. I'll leave this conversation as unresolved and maybe fmayer has an opinion.

I lean towards keeping it simple like this, but a very slight lean.

https://github.com/llvm/llvm-project/pull/112727