Add LLVM core libs packages

[awakecoding]

Summary

• add a dedicated LLVM core libs workflow for Core + BitReader development packages
• produce explicit static/shared artifacts across the LLVM target matrix
• add Windows /MT and /MD variants, with static CRT directive checks and shared LLVM-C.dll dependency/export checks
• wire LLVM core libs artifacts into release downloads and document the artifact naming

Validation

• git diff --check
• YAML parse for .github/workflows/llvm-core-libs.yml
• LLVM core libs workflow run 26709435848: success, 40/40 jobs