[DebugInfo] Stable sort symbols to remove non-deterministic ordering

Summary: This fixes failure in DebugInfo/X86/multiple-aranges.ll uncovered by D39245.

Reviewers: rafael, echristo, probinson

Reviewed By: probinson

Subscribers: probinson, llvm-commits, JDevlieghere

Tags: #debug-info

Differential Revision: https://reviews.llvm.org/D39950

llvm-svn: 326056