[clang] [clang][test] Make libclang CrashTests use threadsafe gtest death-test style (PR #196148)

[Steven Wu via cfe-commits]

cachemeifyoucan wrote:

Going to merge since it happened again in CI https://ci.swift.org/job/llvm.org/job/clang-stage1-RA-as/job/main/1680/testReport/junit/Clang-Unit/libclang_CrashTests___libclangCrashTests_LibclangParseTest/UninstallAbortingLLVMFatalErrorHandler/. The fix is validated to be working from lldb. We can fix other death test when they emerge. 

https://github.com/llvm/llvm-project/pull/196148