Don't update XDG mimetypes during build. This is done by the ports framework.

--- kmymoney/CMakeLists.txt.orig	2017-12-23 22:27:53 UTC
+++ kmymoney/CMakeLists.txt
@@ -114,7 +114,6 @@ install(FILES org.kde.kmymoney.appdata.xml
 install(FILES x-kmymoney.xml
   DESTINATION ${XDG_MIME_INSTALL_DIR})
 
-update_xdg_mimetypes(${XDG_MIME_INSTALL_DIR})
 
 ########## Application Icons #############
 install(DIRECTORY icons/hicolor
