[llvm-cov][gcov] Support multi-files coverage in one basic block (#144504) In the current gcov implementation, all lines within a basic block are attributed to the source file of the block's containing function. This is inaccurate when a block contains lines from other files (e.g., via #include "foo.inc"). Commit [406e81b](https://github.com/llvm/llvm-project/commit/406e81b79d26dae6838cc69d10a3e22635da09ef) attempted to address this by filtering lines based on debug info types, but this approach has two limitations: * **Over-filtering**: Some valid lines belonging to the function are incorrectly excluded. * **Under-counting**: Lines not belonging to the function are filtered out and omitted from coverage statistics. **GCC Reference Behavior** GCC's gcov implementation handles this case correctly.This change aligns the LLVM behavior with GCC. **Proposed Solution** 1. **GCNO Generation**: * **Current**: Each block stores a single GCOVLines record (filename + lines). * **New**: Dynamically create new GCOVLines records whenever consecutive lines in a block originate from different source files. Group subsequent lines from the same file under one record. 2. **GCNO Parsing**: * **Current**: Lines are directly attributed to the function's source file. * **New**: Introduce a GCOVLocation type to track filename/line mappings within blocks. Statistics will reflect the actual source file for each line.
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