Auto merge of #114225 - workingjubilee:only-golden-arches, r=compiler…

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Only golden arches

A number of tests in the test suite have applied the somewhat comedic practice of ignoring *every* single target architecture that rustc has ever supported. This is silly, when they are clearly tests built around certain assumptions, primarily of the x86-64 architecture, or in one case when they are only relevant for a handful of 32-bit targets. This has even resulted, in one case, in the same architecture being ignored twice!

Document these better, and use a "revision + only-arch" idiom in the test headers to denote the "golden arches" that actually pass these tests.