Fix static build with CMAKE_DEBUG_POSTFIX

[Maiyu27]

Description

This patch fixes an issue where building a static version of msquic with CMAKE_DEBUG_POSTFIX set fails during the linking step. Previously, the build would attempt to link a library file without the postfix, causing a fatal LNK1181 error. This change ensures the correct filename with the postfix is used for static builds.

Steps to reproduce

1. Configure a Debug build with QUIC_BUILD_SHARED=OFF and CMAKE_DEBUG_POSTFIX=d.
2. Attempt to build msquic.
3. Observe the linking failure without this fix.

Expected behavior

The build should succeed using the correct library filename with the debug postfix.

Actual behavior

The build fails during linking because the library file without the postfix is referenced.

Notes

• Verified locally.
• Minor change in CMakeLists.txt to respect CMAKE_<CONFIG>_POSTFIX for static builds.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.25%. Comparing base (0b1071e) to head (12d5e17).
⚠️ Report is 35 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5656      +/-   ##
==========================================
- Coverage   85.05%   84.25%   -0.80%     
==========================================
  Files          60       60              
  Lines       18663    18663              
==========================================
- Hits        15873    15725     -148     
- Misses       2790     2938     +148     

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