[embedded] Rename and explain test/embedded/ouroboros-bug.swift

Author: kubamracek

test/embedded/arc-crash.swift renamed to test/embedded/ouroboros-bug.swift

@@ -1,3 +1,8 @@
+// Regression test for a "Ouroboros Bug": The ARC optimizer doesn't like the
+// presense of a direct call to swift_retain and swift_release in any Swift
+// code, but in the embedded Swift's runtime that's somewhat reasonable thing
+// to do (but is to be avoided because of this).
+
 // RUN: %target-swift-frontend -target armv7-apple-none-macho -assert-config Debug -Osize -Xcc -D__MACH__ -emit-ir %s -enable-experimental-feature Embedded | %FileCheck %s
 // RUN: %target-swift-frontend -target arm64-apple-none-macho -assert-config Debug -Osize -Xcc -D__MACH__ -Xcc -D__arm64__ -Xcc -D__APPLE__ -emit-ir %s -enable-experimental-feature Embedded | %FileCheck %s