[llvm] [ThinLTO]Record import type in GlobalValueSummary::GVFlags (PR #87597)

[Mingming Liu via llvm-commits]

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@@ -737,6 +737,7 @@ lltok::Kind LLLexer::LexIdentifier() {
   KEYWORD(live);
   KEYWORD(dsoLocal);
   KEYWORD(canAutoHide);
+  KEYWORD(importAsDec);
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minglotus-6 wrote:

Update to use one-bit state and the enum class [comment](https://github.com/llvm/llvm-project/pull/87597/files#diff-55dc08bb988d556731f68efe4a6d7c40b6cf4acc5a7dd4943ce335f89ce3fea7R435-R446). PTAL, thanks!

Re test coverage
- ThinLTO/X86/dot-dumpler.ll covers ModuleSummaryIndex::exportToDot
- Transforms/WholeProgramDevirt/import-indir.ll covers the update of
  FunctionSummaryTraits, and test both {def, decl}
- Assembler/thinlto-summary tests both {def, decl}
- The rest of test cases are backfill'ed with def and doesn't test decl.

https://github.com/llvm/llvm-project/pull/87597