Add utils: cxref, cflow, ctags

[jgarzik]

No description provided.

[Copilot]

Pull request overview

This PR adds three POSIX C development utilities (cflow, ctags, and cxref) to the posixutils-rs project, along with supporting infrastructure changes.

Purpose: Implement POSIX-compliant C source code analysis tools that generate call flow graphs (cflow), tag files for editors (ctags), and cross-reference tables (cxref). These utilities leverage a newly exported library interface from the existing pcc (POSIX C compiler) crate.

Key Changes:

• Creates a library interface (cc/lib.rs) to share the C parser infrastructure across utilities
• Implements three new utilities with comprehensive integration tests
• Improves m4 test infrastructure to handle parallel test execution and flexible binary paths

Reviewed changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 9 comments.

Show a summary per file

File	Description
cc/lib.rs	New library interface exposing C parser, tokenizer, and related infrastructure for use by cflow, ctags, and cxref
cc/cflow.rs	Implementation of cflow utility that generates C-language flowgraphs showing function call relationships
cc/ctags.rs	Implementation of ctags utility that creates tag files for vi/ex editors, recognizing functions, typedefs, and macros
cc/cxref.rs	Implementation of cxref utility that generates cross-reference tables showing symbol definitions and uses
cc/Cargo.toml	Adds library target and three new binary targets for the new utilities
cc/tests/integration.rs	Adds test module declarations for the three new utilities
cc/tests/cflow/mod.rs	Integration tests for cflow covering basic operation, depth limits, reverse mode, and output format
cc/tests/cflow/test.c	Test fixture C source file for cflow tests
cc/tests/ctags/mod.rs	Integration tests for ctags covering basic tagging, index mode, append mode, and sorted output
cc/tests/ctags/test.c	Test fixture C source file for ctags tests
cc/tests/cxref/mod.rs	Integration tests for cxref covering symbol detection, definitions, silent mode, and output files
cc/tests/cxref/test.c	Test fixture C source file for cxref tests
lib/utils.tsv	Registers the three new utilities in the project's utility index
README.md	Moves cflow, ctags, and cxref from "Stage 0 - Not started" to completed Development utilities
m4/tests/integration_test.rs	Improves test infrastructure with proper workspace detection, race-free cargo builds using Once, and support for both debug and release binaries