Refactor PIE buildmode setup

[mowies]

During my time in rebase-hell for #762 after #726 was merged, I noticed that the PIE buildmode setup with duplicated builds with lots of ignored arch/os combinations could be simplified a lot with a different approach:

Instead of using build combinations to encode the compatible architectures where PIE binaries are possible, it can be encoded into a templated environment variable similar to what is described here in the goreleaser docs. That env variable could then be used directly in the ldflags like is done here to get the same result without the need to duplicate builds.

cc @jackgopack4

[mx-psi]

This makes sense to me