`swift test` tries to build all targets instead of just those needed for testing

[bbrk24]

@Geordie_J

For example, if devs don’t have PostgreSQL server installed then our build would still fail because there’s no „winning“ unsafe flags we could reasonably provide. (see also: build performance). We‘re talking about a „very optional“ product that I’d even argue should not be built, most of the time.

For some projects it's even worse: take, for example, swift-cross-ui. You will never be able to build every single target on one machine because some targets require Apple-only dependencies (e.g. AppKit) while others require the Windows SDK. So simply running swift test will never work.