riscv: Require clang-17 or newer for kCFI

riscv: Require clang-17 or newer for kCFI

After the combination of commit c217157bcd1d ("riscv: Implement
HAVE_DYNAMIC_FTRACE_WITH_CALL_OPS"), which starts using
'-fpatchable-function-entry=M,N', and commit d0262e907e29 ("riscv:
ftrace: support PREEMPT"), which allows CONFIG_DYNAMIC_FTRACE to be
enabled by allmodconfig, allmodconfig builds with clang-16 begin
crashing in the generic LLVM kCFI pass (see [1] for the stack trace).

clang-17 avoids this crash by moving to target-specific lowering of the
kCFI operand bundles [2]. Require clang-17 to select CONFIG_CFI_CLANG to
avoid this crash.

Fixes: c217157bcd1d ("riscv: Implement HAVE_DYNAMIC_FTRACE_WITH_CALL_OPS")
Link: https://godbolt.org/z/xG39Pn16o
Link: https://github.com/llvm/llvm-project/commit/62fa708ceb027713b386c7e0efda994f8bdc27e2
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Link: https://lore.kernel.org/r/20250612-riscv-require-clang-17-for-kcfi-v1-1-216f7cd7d87f@kernel.org
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>