[clang] [RISCV] Implement shadow stack on shadow stack mode with Zicfiss. (PR #68075)

[Paul Kirth via cfe-commits]

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@@ -27,6 +27,11 @@
 
 using namespace llvm;
 
+static cl::opt<bool>
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ilovepi wrote:

 is it possible to use something other than a `cl::opt`? I know we make heavy use of them to control codegen options, but they tend to get dropped on the floor easily if you have to forward `-mllvm` options to the linker in LTO/ThinLTO builds. This is a constant pain point for a lot of folks who need to support multiple build configurations, like the Linux kernel, Fuchsia, Android, or Chrome. 

https://github.com/llvm/llvm-project/pull/68075