[clang] [llvm] [NFC][RootSignatures] Conform to new std::optional calling conventions (PR #136747)

[Damyan Pepper via cfe-commits]

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@@ -236,6 +278,102 @@ TEST_F(ParseHLSLRootSignatureTest, InvalidParseUnexpectedEndOfStreamTest) {
 
   // Test correct diagnostic produced - end of stream
   Consumer->setExpected(diag::err_expected_after);
+
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damyanp wrote:

It's kind of surprising to see all these new tests (and a bunch of new functional code above) added for something that's called NFC.

https://github.com/llvm/llvm-project/pull/136747