Switch swift-evolve XFAILs to UNSUPPORTEDs

These tests may not *reliably* fail with shuffled standard libraries, so we can’t use XFAIL, which fails if the test succeeds.

Author: beccadax

test/SIL/Parser/array_roundtrip.swift

@@ -2,6 +2,6 @@
 
 // Fails if the positions of the two Collection subscript requirements are
 // reversed. rdar://problem/46650834
-// XFAIL: swift_evolve
+// UNSUPPORTED: swift_evolve
 
 var W = [UInt32](repeating: 0, count: 16)

test/api-digester/stability-stdlib-abi.swift

@@ -11,4 +11,4 @@
 // order into the ABI. rdar://problem/46617463
 // The digester can incorrectly register a generic signature change when
 // declarations are shuffled. rdar://problem/46618883
-// XFAIL: swift_evolve
+// UNSUPPORTED: swift_evolve