[llvm] [clang] [RISCV] Add Zicfiss support to the shadow call stack implementation. (PR #68075)

[Yeting Kuo via cfe-commits]

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@@ -151,9 +155,10 @@ Usage
 
 To enable ShadowCallStack, just pass the ``-fsanitize=shadow-call-stack`` flag
 to both compile and link command lines. On aarch64, you also need to pass
-``-ffixed-x18`` unless your target already reserves ``x18``. On RISC-V, ``x3``
-(``gp``) is always reserved. It is, however, important to disable GP relaxation
-in the linker. This can be done with the ``--no-relax-gp`` flag in GNU ld.
+``-ffixed-x18`` unless your target already reserves ``x18``. On RISC-V with software
+shadow stack, ``x3`` (``gp``) is always reserved. It is, however, important to
+disable GP relaxation in the linker. This can be done with the ``--no-relax-gp``
+flag in GNU ld.
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yetingk wrote:

Done. Thank you for your suggestion.

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