[Test] Temporarily mark typeref_decoding.swift as unsupported

This seems to be failing on Linux aarch64 on and off. Mark unsupported
while we investigate.

Author: bnbarham

test/Reflection/typeref_decoding.swift

@@ -9,7 +9,7 @@
 // RUN: %empty-directory(%t)
 
 // FIXME: rdar://127796117
-// XFAIL: OS=linux-gnu && CPU=aarch64
+// UNSUPPORTED: OS=linux-gnu && CPU=aarch64
 
 // RUN: %target-build-swift -Xfrontend -enable-anonymous-context-mangled-names %S/Inputs/ConcreteTypes.swift %S/Inputs/GenericTypes.swift %S/Inputs/Protocols.swift %S/Inputs/Extensions.swift %S/Inputs/Closures.swift -parse-as-library -emit-module -emit-library -module-name TypesToReflect -o %t/%target-library-name(TypesToReflect)
 // RUN: %target-build-swift -Xfrontend -enable-anonymous-context-mangled-names %S/Inputs/ConcreteTypes.swift %S/Inputs/GenericTypes.swift %S/Inputs/Protocols.swift %S/Inputs/Extensions.swift %S/Inputs/Closures.swift %S/Inputs/main.swift -emit-module -emit-executable -module-name TypesToReflect -o %t/TypesToReflect