[clang] [llvm] [RISCV] Enable TLSDESC by default (PR #166540)

[Jessica Clarke via llvm-commits]

jrtc27 wrote:

Please limit this to Linux. Nobody's yet done the work to support it on FreeBSD, and I assume that's true of basically every OS other than Linux. I don't even know if musl supports it; the burden is on you to verify which implementations support TLSDESC (and have done for long enough that we can assume support by default) and enable only those ones.

https://github.com/llvm/llvm-project/pull/166540