[llvm] [LoongArch] Emit function call code sequence as `PCADDU18I+JIRL` in medium code model (PR #76555)

[WÁNG Xuěruì via llvm-commits]

https://github.com/xen0n commented:

The test case name `no-schedue` could be something more descriptive like "psabi-restricted-scheduling".

Overall it's mostly good and patch no. 1 is LGTM, thanks!

https://github.com/llvm/llvm-project/pull/76555