[llvm] [ADT] Add back ability to compare StringSet (PR #91374)

[Jakub Kuderski via llvm-commits]

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@@ -73,4 +73,12 @@ TEST_F(StringSetTest, Contains) {
   EXPECT_FALSE(Set.contains("test"));
 }
 
+TEST_F(StringSetTest, Equal) {
+  StringSet<> A = {"A"};
+  StringSet<> B = {"B"};
+  ASSERT_TRUE(A != B);
+  ASSERT_FALSE(A == B);
+  ASSERT_TRUE(A == A);
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kuhar wrote:

this seem redundant

https://github.com/llvm/llvm-project/pull/91374