[DWARF][RISCV] Test resolving of RISC-V relocations

Summary: This patch adds an object file (in yaml format) with a synthetic
.debug_info section which we use to test that the supported RISC-V relocations
are properly resolved.

Reviewers: asb, lenary, MaskRay
Reviewed By: MaskRay
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D70541