[llvm-profgen][NFC] Fix test failure by making unwinder's output deterministic

Don't know why under Sanitizer build(asan/msan/ubsan), the `std::unordered_map<string, ...>`'s output order is reversed, make the regression test failed.

This change creates a workaround by using sorted container to make the output deterministic.

Reviewed By: hoy, wenlei

Differential Revision: https://reviews.llvm.org/D92816