windows: restore CreateSymbolicLink declarations and conformance coverage

[GGRei]

Summary

• Add the canonical CreateSymbolicLinkA/W declarations and flags to the Windows headers.
• Add the missing CreateSymbolicLinkA export while preserving all existing bundled exports.
• Apply the source fix reproducibly through build.ps1.
• Add strict C-only x64 and i386 CI probes covering declarations, calling conventions and linking.

Validation

• The source patch reproduces the checked-in header byte-for-byte.
• x64 and i386 probes compile and link successfully.
• Both CreateSymbolicLinkA and CreateSymbolicLinkW imports were verified.
• codex review and CI green