fix/issue-3101: fix the issue of mdc ignores SPDLOG_NO_TLS

[Allen-20180115]

Dear Spdlog author and Spdlog maintainers,
I hope this message finds you well. I have noticed issue #3101 titled "MDC ignores SPDLOG_NO_TLS" and believe I have found a solution that might address the problem described.
I have submitted a Pull Request (PR) with the following details:
● PR Title: Brief description of the changes made.
● Commit Message: Detailed explanation of the changes, including the approach taken and any tests performed.
● Related Issue: Resolves issue #3101 by implementing the aforementioned changes.
In my PR, I have made the following changes:
● [List of changes made in the PR, e.g., "Fix the issue of mdc ignores SPDLOG_NO_TLS"].
● [Any additional changes or relevant details].

Test environment and compilation steps:
OS: Ubuntu 18.04 LTS
Architecture: x86-64
Compiler: gcc 7.5.0

Test results of the original main branch code:

I have tested the solution using the example program from the spdlog library, and it proves to work correctly. If necessary, I can provide more persuasive test results later on and believe it aligns with the project's coding standards. However, I am open to any feedback or suggestions for improvement. If there are any adjustments needed, or if further clarification is required, please let me know.
Thank you for considering my contribution. I am excited about the opportunity to contribute to Spdlog and look forward to your review.
Best regards,
[Allen/Allen-20180115]

[gabime]

Thanks for the PR. I think however that the fix can be much simpler: just wrap the code inside mdc.h code with #ifndef SPDLOG_NO_TLS (and the code in the format function).

[Allen-20180115]

Thanks for the PR. I think however that the fix can be much simpler: just wrap the code inside mdc.h code with #ifndef SPDLOG_NO_TLS (and the code in the format function).

I am delighted to receive your response. I agree that the modification to the function signature of get_context in the mdc.h file has a significant impact. Although it has passed simple tests and works normally, it is indeed not a good solution. After revisiting the code involving the mdc file and the compile option SPDLOG_NO_TLS in the spdlog library, and considering your perspective (which I had also thought of but not attempted), I have revised the related code and resubmitted a new PR. I hope this will be helpful in resolving the issue. Thank you!