Fix x509-store for illumos

[gwr]

Can't use sizof(d->d_name)
Use NAME_MAX or MAXNAMLEN

Without this, the code running on illumos reads only 1 character of the file names in the certificates store and cannot find any certificates.

[gwr]

This is a prerequisite for using System.Net.Security on illumos.

[dotnet-policy-service]

Tagging subscribers to this area: @bartonjs, @vcsjones, @dotnet/area-system-security
See info in area-owners.md if you want to be subscribed.

[Copilot]

Pull request overview

Updates native X509 store enumeration to avoid relying on sizeof(dirent.d_name) (which is not usable on illumos) when allocating buffers and handling certificate file names.

Changes:

• Compute the temporary path buffer size using NAME_MAX / MAXNAMLEN (with a fallback) instead of sizeof(d_name).
• Add a guard to skip .pfx entries whose names won’t fit in the remaining buffer space.
• Switch filename length computation from strnlen(..., sizeof(d_name)) to strlen(...).

[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.

[bartonjs]

/azp run runtime-libraries-coreclr outerloop

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).