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

[Yueh-Ting Chen via cfe-commits]

eopXD wrote:

> > Maybe test coverage with `-I %resource_dir`?
> 
> Which file should I place the test?

`clang/test/Headers/`

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