They both can mean the same thing but they are not the same. Probably a similar problem to 目標 and 目的.
The main difference to me is the point of view.
- User's point of view => 要求
- Dev's point of view => 要件
要求 would be functionalities the user is looking for. While 要件 would be functionalities the system need to do to answer the 要求.
In my company, we first go through the 要求開発 process, which can include customer study, market survey etc to decide what functionality to add to our product. Then it is passed to a 要件定義 that clearly define the specifications of your product.
要求 is not supposed to be done in the 開発部 but by the 営業／マーケティング部.
I don't fully get the other two meanings but
- Minimum system requirements : 要求スペック