[llvm] [clang] [RISCV] Add sifive-p450 CPU. (PR #75760)

[Wang Pengcheng via cfe-commits]

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@@ -222,6 +222,11 @@
 // MCPU-SIFIVE-X280-SAME: "-target-feature" "+zvl512b" "-target-feature" "+zvl64b"
 // MCPU-SIFIVE-X280-SAME: "-target-abi" "lp64d"
 
+// RUN: %clang -target riscv64 -### -c %s 2>&1 -menable-experimental-extensions -mcpu=sifive-p450 | FileCheck -check-prefix=MCPU-SIFIVE-P450 %s
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wangpc-pp wrote:

Are there any `experimental` extensions?

https://github.com/llvm/llvm-project/pull/75760