gentoo-overlay/media-gfx/darktable/files/darktable-3.4.1_libxcf-cmake.patch

--- a/src/external/CMakeLists.txt
+++ b/src/external/CMakeLists.txt
@@ -1,5 +1,16 @@
 if(USE_XCF)
-  add_subdirectory(libxcf)
+#  find_package(ZLIB REQUIRED)
+  add_library(xcf STATIC
+    "${CMAKE_CURRENT_SOURCE_DIR}/libxcf/xcf.c"
+    "${CMAKE_CURRENT_SOURCE_DIR}/libxcf/xcf.h"
+    "${CMAKE_CURRENT_SOURCE_DIR}/libxcf/xcf_names.c"
+    "${CMAKE_CURRENT_SOURCE_DIR}/libxcf/xcf_names.h"
+  )
+  set_property(TARGET xcf PROPERTY C_STANDARD 99)
+  target_compile_definitions(xcf PRIVATE _DEFAULT_SOURCE) # needed for htobe*()
+  target_include_directories(xcf PUBLIC "${CMAKE_CURRENT_SOURCE_DIR}/libxcf")
+#  target_link_libraries(xcf PUBLIC ZLIB::ZLIB)
+#  target_link_libraries(xcf PUBLIC m)
 endif()
 
 add_library(whereami STATIC "${CMAKE_CURRENT_SOURCE_DIR}/whereami/src/whereami.c")