CMake: Fix OPTION_DOCS_ONLY mode

CMakeLists.txt

@@ -86,6 +86,18 @@ if(OPTION_TOOLS_ONLY)
         unset(HOST_BINARY_DIR CACHE)
     endif()
     add_subdirectory(${CMAKE_SOURCE_DIR}/src)
+
+    # Cut down find_version which doesn't include cfg defines set in full configure
+    add_custom_target(find_version
+            ${CMAKE_COMMAND}
+                    -DFIND_VERSION_BINARY_DIR=${CMAKE_BINARY_DIR}/generated
+                    -DCPACK_BINARY_DIR=${CMAKE_BINARY_DIR}
+                    $<$<PLATFORM_ID:Windows>:-DWIN32=TRUE>
+                    -P "${CMAKE_SOURCE_DIR}/cmake/scripts/FindVersion.cmake"
+            WORKING_DIRECTORY ${CMAKE_SOURCE_DIR}
+            BYPRODUCTS ${GENERATED_SOURCE_FILES}
+    )
+
     return()
 endif()