[llvm-objdump,test] Fix source-interleave.ll when /proc/self/cwd is unavailable

e.g. on Mach-O

Suppress spurious warnings due to R_RISCV_SET_ULEB128

llvm-objdump -S issues unnecessary warnings for RISC-V relocatable files
containing .debug_loclists or .debug_rnglists sections with ULEB128
rel

Suppress spurious warnings due to R_RISCV_SET_ULEB128

llvm-objdump -S issues unnecessary warnings for RISC-V relocatable files
containing .debug_loclists or .debug_rnglists sections with ULEB128
relocations. This occurred because `DWARFObjInMemory` verifies support for all
relocation types, triggering warnings for unsupported ones.

```
% llvm-objdump -S a.o
...
0000000000000000 <foo>:
warning: failed to compute relocation: R_RISCV_SUB_ULEB128, Invalid data was encountered while parsing the file
warning: failed to compute relocation: R_RISCV_SET_ULEB128, Invalid data was encountered while parsing the file
...
```

This change fixes #101544 by declaring support for the two ULEB128
relocation types, silencing the spurious warnings.

---

In DWARF v5 builds, DW_LLE_offset_pair/DW_RLE_offset_pair might be
generated in .debug_loclists/.debug_rnglists with ULEB128 relocations.
They are only read by llvm-dwarfdump to dump section content and verbose
DW_AT_location/DW_AT_ranges output for relocatable files.

The DebugInfoDWARF user (e.g. DWARFDebugRnglists.cpp) calls
`Data.getULEB128` without checking the ULEB128 relocations, as the
unrelocated value holds meaning (refer to the assembler
implementation https://reviews.llvm.org/D157657). This differs from
`.quad .Lfoo`, which requires relocation reading (e.g.
https://reviews.llvm.org/D74404).

Pull Request: https://github.com/llvm/llvm-project/pull/101607

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