Fix macOS strerror_r incompatibility

[UnsaltedHash42]

This patch corrects the use of for POSIX platforms like macOS, which return an int instead of a char*. Fix tested on macOS 14.3 (ARM64).

[ToruNiina]

The problem you are trying to fix existed in a version of toml11 from two years ago, and no longer exists. Although another contributor fixed it at the time, toml11 has released a major update, and much of the code related to this problem has been extensively rewritten.

Your patch is designed to be applied to the code as it was two years ago, and will simply break the current codebase if applied now. I have already given permission for the CI to run, so please check the results.

I followed the link to see why you submitted this patch, and it seems that you ran into errors trying to build another project on MacOS. This project references the toml11 version from two years ago. So a more constructive approach would be to update the toml11 version referenced by the original repository to the latest version.

After the git pull in the client/external/toml11 submodule, change line 33 in client/CMakeLists.txt from include_directories(external/toml11) to include_directories(external/toml11/include).
For most use cases where a file is read but not serialised, code changes are often unnecessary to update toml11 from v3 to v4.