[llvm-debuginfo-analyzer] Pass references instead of pointers (Comparison functions).

[CarlosAlbertoEnciso]

Extracted from llvm/tools/llvm-debuginfo-analyzer/README.txt
https://reviews.llvm.org/D125782#inline-1293920

In the comparison functions, pass references instead of pointers (when
pointers cannot be null).

[llvmbot]

@llvm/issue-subscribers-debuginfo

Author: Carlos Alberto Enciso (CarlosAlbertoEnciso)

Extracted from [llvm/tools/llvm-debuginfo-analyzer/README.txt](https://github.com/llvm/llvm-project/blob/main/llvm/tools/llvm-debuginfo-analyzer/README.txt) https://reviews.llvm.org/D125782#inline-1293920

In the comparison functions, pass references instead of pointers (when
pointers cannot be null).