[clang] [RISCV] Enable GP relaxation for Linux (PR #201265)

[Pengcheng Wang via cfe-commits]

wangpc-pp wrote:

> The GP relaxation in lld only works for medlow without PIC. Linux defaults to PIE usually doesn't it?

Get it. Does the gcc in OS distros also default to PIE?

https://github.com/llvm/llvm-project/pull/201265