[llvm] [RISCV] Support Global Dynamic TLSDESC in the RISC-V backend (PR #66915)

[Paul Kirth via llvm-commits]

ilovepi wrote:

ping. @topperc @jrtc27 @asb can we take a look at this? psABI has approved TLSDESC, and there are patches out for GCC and binutils. 

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