[compiler-rt][test] Fix flake in symbolize_stack test

Addresses tests flakes described in
https://github.com/llvm/llvm-project/issues/55460

The test being updated can fail in FileCheck to match when given long
enough stack traces. This can be problematic when file system paths
become long enough to cause the majority of the long function name to
become truncated. We found in our CI that the truncated output would
often fail to match, thereby causing the test to fail when it should not.

Here we change the test to match on sybolizer output that should be more
reliable than matching inside the long function name.

Reviewed By: vitalybuka

Differential Revision: https://reviews.llvm.org/D126102