sema: accept an array literal of enum case references as compile-time constant

test/Sema/const_enum_elements_array.swift

@@ -0,0 +1,20 @@
+// RUN: %target-typecheck-verify-swift
+
+enum E {
+  case a
+  case b
+
+  var z: E { .b }
+}
+
+func getAE() -> E { return .a }
+
+func test_without_const(_ : [E]) {}
+func testArr(_ : _const [E]) {}
+
+testArr([])
+testArr([.a])
+testArr([.a, .b])
+
+testArr([getAE()]) // expected-error {{expect a compile-time constant literal}}
+testArr([.a, .b, .a.z]) // expected-error {{expect a compile-time constant literal}}