[RISCV] Consume error from parsing attributes section

Summary:
We don't consume the error from getBuildAttributes, so an assertions
build crashes with "Program aborted due to an unhandled Error:".
Explicitly consume it like the ARM version in that case.

Reviewers: asb, jhenderson, MaskRay, HsiangKai

Reviewed By: MaskRay

Subscribers: kristof.beyls, hiraditya, simoncook, kito-cheng, shiva0217, rogfer01, rkruppe, psnobl, benna, Jim, lenary, s.egerton, sameer.abuasal, luismarques, evandro, danielkiss, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D77841