Add a news entry for macOS SDK directory change

See conda-forge/conda-smithy#2430.

Signed-off-by: Michał Górny <[email protected]>

Author: mgorny

news/2025-12-04-osx-sdk-dir.md

@@ -0,0 +1,5 @@
+# macOS SDK directory changed
+
+Starting with conda-smithy 3.53.4, the build scripts will no longer use the system macOS SDK directory by default. The CI systems will use a dedicated `/opt/conda-sdks` directory, while users performing local builds will need to choose a writable directory, and provide the path to it via `OSX_SDK_DIR` environment variable.
+
+This change may result in some build systems, particularly CMake, storing paths to this temporary build directory in installed metadata. Feedstocks will need to substitute the stored paths with path-agnostic solutions (for example, see [substitutions in openpmd-api-feedstock](https://github.com/conda-forge/openpmd-api-feedstock/blob/15f9b3648f087d3e06331d6ec9ddff0710300593/recipe/build.sh#L100-L107)) or the correct sysroot paths (for example, see [substitutions in cartographer-feedstock](https://github.com/conda-forge/cartographer-feedstock/blame/1812f8c13bccbad20daf6ba079f7722cace93a15/recipe/conda_build_config.yaml#L19-L23).