chore: fix C lint errors (issue #6475)

[sahilk45]

Resolves #6475

Description

What is the purpose of this pull request?

This PR addresses C linting issues in benchmark.length.c by replacing variable-length arrays (VLAs) with dynamically allocated memory.

• Replaced VLAs (double x[len];) with dynamic memory allocation (malloc) for better compatibility and avoiding potential stack overflows.
• Added memory allocation failure checks to prevent undefined behavior.
• Ensured proper memory deallocation (free) at the end of execution.
• Initialized all variables at declaration to prevent uninitialized variable warnings.

Related Issues

Does this pull request have any related issues?

This pull request:

• resolves Fix C lint errors #6475

Questions

Any questions for reviewers of this pull request?

Can we prefer using VLAs (which are valid in C99) ?

Other

Any other information relevant to this pull request? This may include screenshots, references, and/or implementation notes.

No.

Checklist

Please ensure the following tasks are completed before submitting this pull request.

• Read, understood, and followed the contributing guidelines.

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[stdlib-bot]

Coverage Report

Package	Statements	Branches	Functions	Lines
strided/base/dmap	$\color{green}206/206$ $\color{green}+100.00\%$	$\color{green}9/9$ $\color{green}+100.00\%$	$\color{green}2/2$ $\color{green}+100.00\%$	$\color{green}206/206$ $\color{green}+100.00\%$

The above coverage report was generated for the changes in this PR.

[sahilk45]

@kgryte Thank you for suggestion. PLease review it again I made the asked changes. Let me know if anything else is still requires.
regards,
SAHIL KUMAR