Fix GSYM tests to run the yaml files and fix test failures on some machines.

Fix GSYM tests to run the yaml files and fix test failures on some machines.

Summary: YAML files were not being run during lit testing as there was no lit.local.cfg file. Once this was fixed, some buildbots would fail due to a StringRef that pointed to a std::string inside of a temporary llvm::Triple object. These issues are fixed here by making a local triple object that stays around long enough so the StringRef points to valid data.

Reviewers: aprantl, thakis, MaskRay, aadsm, wallace

Subscribers: llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D75390