[llvm] [ThinLTO][BitcodeWriter] Write import type in per-module combined summary (PR #87600)

[Jan Voung via llvm-commits]

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@@ -428,6 +428,10 @@ class IndexBitcodeWriter : public BitcodeWriterBase {
   /// The combined index to write to bitcode.
   const ModuleSummaryIndex &Index;
 
+  /// For each module, provides the set of global value summaries for which the
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jvoung wrote:

nit: maybe indicate "When writing a subset of the index" also?

https://github.com/llvm/llvm-project/pull/87600