[Driver] Error for -gsplit-dwarf with RISC-V linker relaxation

-gsplit-dwarf produces a .dwo file which will not be processed by the linker. If
.dwo files contain relocations, they will not be resolved. Therefore the
practice is that .dwo files do not contain relocations.

Address ranges and location description need to use forms/entry kinds indexing
into .debug_addr (DW_FORM_addrx/DW_RLE_startx_endx/etc), which is currently not
implemented.

There is a difficult-to-read MC error with -gsplit-dwarf with RISC-V for both -mrelax and -mno-relax.
```
% clang --target=riscv64-linux-gnu -g -gsplit-dwarf -c a.c
error: A dwo section may not contain relocations
```

We expect to fix -mno-relax soon, so report a driver error for -mrelax for now.

Link: https://github.com/llvm/llvm-project/issues/56642

Reviewed By: compnerd, kito-cheng

Differential Revision: https://reviews.llvm.org/D130190