Add explicit buffer bounds check and fix some functions

[markj]

Summary

This change adds explicit buffer bounds checks to functions that write strings into buffers, replacing unsafe operations such as strcpy with safer alternatives using size checks and std::copy. It also ensures section and segment names do not overflow their target fields and adds error handling for negative offsets. These changes address potential buffer overflow vulnerabilities and make the code robust against out-of-bounds memory access.

Test Plan

Run static analyzers (such as Snyk ,and my hands)

[markj]

This isn't the right place to submit changes to llvm. This copy of llvm is imported from https://github.com/llvm/llvm-project and changes should be proposed there.