Fix how to get the verilator directory

David Kennedy Souza Araújorequested to merge
davidkennedydev/caster:fix_verilator_root_dir into master

Modify the build script (Makefile) to retrieve the Verilator ROOT directory using the CLI's proper option.

FYI: The original implementation fails on Fedora 42 when using Verilator installed via DNF5 (the default package manager).

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