build: add Windows 3.14t build flags - CMAKE_C_FLAGS was modifying defaults, CMAKE_C_FLAGS_INIT preserves them

Author: paultiq

.github/workflows/packaging_wheels.yml

@@ -45,9 +45,6 @@ jobs:
           - { minimal: true, python: cp311 }
           - { minimal: true, python: cp312 }
           - { minimal: true, platform: { arch: universal2 } }
-          # Windows+cp314t disabled due to test failures in CI. 
-          # TODO: Diagnose why tests fail (access violations) in some configurations
-          - { python: cp314t, platform: { os: windows-2025 } }  
 
     runs-on: ${{ matrix.platform.os }}
     env:

pyproject.toml

@@ -123,6 +123,15 @@ if.env.COVERAGE = false
 inherit.cmake.define = "append"
 cmake.define.DISABLE_UNITY = "1"
 
+[[tool.scikit-build.overrides]]
+if.platform-system = "^win32"
+if.abi-flags = "t"
+inherit.cmake.define = "append"
+# /DPy_GIL_DISABLED: needed else the build will try to link python314.lib
+# CMAKE_..._FLAGS_INIT not FLAGS: otherwise, msbuild will disable important defaults such as /EHsc
+cmake.define.CMAKE_C_FLAGS_INIT="/DPy_MOD_GIL_USED /DPy_GIL_DISABLED"
+cmake.define.CMAKE_CXX_FLAGS_INIT="/DPy_MOD_GIL_USED /DPy_GIL_DISABLED"
+
 [tool.scikit-build.sdist]
 include = [
     "README.md",