[clang] [RISCV] Install sifive_vector.h to riscv-resource-headers (PR #66330)

[Yueh-Ting Chen via cfe-commits]

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+// RUN: %clang_cc1 -triple riscv64 -target-feature +v %s
+// REQUIRES: riscv-registered-target
+
+// expected-no-diagnostics
+
+#include <sifive_vector.h>
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eopXD wrote:

Does this test case help verify we have `sifive_vector.h` installed?

https://github.com/llvm/llvm-project/pull/66330