Generate a CMake file that locates the debian13 dependencies

Install ${PREFIX}/share/source-stack/source-stack.cmake as the last step. It
mirrors the image's ENV block (prefix, pkg-config and library paths) for
CMake and can restrict lookups to the prefix with GW_SOURCE_STACK_ONLY.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

debian13/Dockerfile

@@ -820,4 +820,10 @@ RUN --mount=type=bind,from=sources,source=duckdb-v1.5.6.tar.gz,target=/tmp/duckd
     && cmake --build build --parallel "$(nproc)" --target install \
     && rm -rf build src ui-src
 
+COPY source-stack.cmake.in /tmp/
+RUN mkdir -p ${PREFIX}/share/source-stack \
+    && sed "s|@MULTIARCH@|$(gcc -dumpmachine)|" /tmp/source-stack.cmake.in \
+        > ${PREFIX}/share/source-stack/source-stack.cmake \
+    && rm /tmp/source-stack.cmake.in
+
 CMD ["/bin/bash"]