[clang] [clang] Add support for `__declspec(no_init_all)` (PR #116847)

[Daniel Paoliello via cfe-commits]

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@@ -8719,6 +8719,18 @@ Attribute used by `clspv`_ (OpenCL-C to Vulkan SPIR-V compiler) to identify func
 }];
 }
 
+def NoTrivialAutoVarInitDocs : Documentation {
+  let Category = DocCatDecl;
+  let Content = [{
+The ``__declspec(no_init_all)`` attribute disables the automatic initialization that the
+`-ftrivial-auto-var-init`_ flag would have applied to locals in a marked function, or instances of
+a marked type. Note that this attribute has no effect for locals that are automatically initialized
+without the `-ftrivial-auto-var-init`_ flag.
+
+.. _`-ftrivial-auto-var-init`: https://clang.llvm.org/docs/ClangCommandLineReference.html#cmdoption-clang-ftrivial-auto-var-init
----------------
dpaoliello wrote:

I've made the link relative, but I have no idea how to get the `:ref:` syntax to work.

In theory it's a link to an option: <https://www.sphinx-doc.org/en/master/usage/referencing.html#role-option>, but it's also cross-doc, so ``:option:`-ftrivial-auto-var-init <ClangCommandLineReference:-ftrivial-auto-var-init=<arg>>` `` should work, but it didn't seem to.

https://github.com/llvm/llvm-project/pull/116847