textproc/fcitx5-m17n: Fix build by depending on ECM directly

The top-level CMakeLists.txt calls find_package(ECM REQUIRED 1.0.0), but
the port never declared the dependency. It only built because
textproc/fcitx5 pulled ECM in at run time. Since 95f9a6808973 dropped
the ECM run dependency, explicitly depending on gettext and ecm is
required (and correct).