[libcxx] [libc] [lldb] [lld] [llvm] [libcxxabi] [clang-tools-extra] [compiler-rt] [flang] [clang] [RISCV] Support Global Dynamic TLSDESC in the RISC-V backend (PR #66915)

[Paul Kirth via cfe-commits]

ilovepi wrote:

@topperc @MaskRay , do either of you have strong feelings about abandoning this in favor of https://github.com/llvm/llvm-project/pull/77515? That PR was made w/ `spr` and should be a bit easier to understand/review (since it won't have merge or fixup commits) and will make the LLD side changes easier to stack.

https://github.com/llvm/llvm-project/pull/66915