[llvm-branch-commits] [LoongArch][Codegen] Add support for TLSDESC (PR #90157)

[via llvm-branch-commits]

https://github.com/wangleiat created https://github.com/llvm/llvm-project/pull/90157

The implementation only enables when the `-enable-tlsdesc` option is
passed and the TLS model is `dynamic`.

LoongArch's GCC has the same option(-mtls-dialet=) as RISC-V.