[ThinLTO] Rename index IsAnalysis flag to HaveGVs (NFC)

With the upcoming patch to add summary parsing support, IsAnalysis would
be true in contexts where we are not performing module summary analysis.
Rename to the more specific and approprate HaveGVs, which is essentially
what this flag is indicating.

llvm-svn: 334140

llvm/lib/Bitcode/Reader/BitcodeReader.cpp

@@ -5779,8 +5779,7 @@ Expected<std::unique_ptr<ModuleSummaryIndex>> BitcodeModule::getSummary() {
   BitstreamCursor Stream(Buffer);
   Stream.JumpToBit(ModuleBit);
 
-  auto Index =
-      llvm::make_unique<ModuleSummaryIndex>(/*IsPerformingAnalysis=*/false);
+  auto Index = llvm::make_unique<ModuleSummaryIndex>(/*HaveGVs=*/false);
   ModuleSummaryIndexBitcodeReader R(std::move(Stream), Strtab, *Index,
                                     ModuleIdentifier, 0);