What goes first architecture or SDLC processes?

Let's start with definitions to use a common ground in further discussion:
Architecture - a definition of a system (i.e. technical proposal) that is enough to be implemented by Devs.
SDLC processes - various processes used in software delivery (e.g. QA, versioning, deployment).

Developing architecture (whatever approach is used) is a part of SDLC. One of the first its stages.
While developing architecture we do care about maintenance and implementation costs but don't care about their details.
The next stages in SDLC are how to deliver this architecture. Each consequent stage cares about the previous one.