NeuroVoider

Glitched weapons are dropped as random loot by killed enemies. When you pick them up, you can identify them via the little pop-up in the top left corner. Glitched weapons are also highlighted in purple colour in your inventory, which is selectable after each level.
Collect and equip two of them to get the achievement. The achievement will pop when you have actually saved your build and progress to the next level.