ifneq - filter

ifneq ($(filter eng user userdebug tests,$(MAKECMDGOALS)),)
  echo "abcdefg"
endif

$(filter eng user userdebug tests,$(MAKECMDGOALS))是檢查$(MAKECMDGOALS)中有没有eng user userdebug tests這些字串，有的話返回字串。

所以ifneq ($(filter eng user userdebug tests,$(MAKECMDGOALS)),)可以這樣理解
當make後输入的命令有eng / user / userdebug / tests這些字串，條件成立，執行後面語句，error中斷make，否则條件不成立，make繼續前進

ref : Here