[IR] Disallow llvm.global_ctors and llvm.global_dtors of the 2-field form in textual format

The 3-field form was introduced by D3499 in 2014 and the legacy 2-field
form was planned to be removed in LLVM 4.0

For the textual format, this patch migrates the existing 2-field form to
use the 3-field form and deletes the compatibility code.
test/Verifier/global-ctors-2.ll checks we have a friendly error message.

For bitcode, lib/IR/AutoUpgrade UpgradeGlobalVariables will upgrade the
2-field form (add i8* null as the third field).

Reviewed By: rnk, dexonsmith

Differential Revision: https://reviews.llvm.org/D61547

llvm-svn: 360742

llvm/lib/Bitcode/Reader/BitcodeReader.cpp

@@ -2794,8 +2794,14 @@ Error BitcodeReader::globalCleanup() {
   }
 
   // Look for global variables which need to be renamed.
+  std::vector<std::pair<GlobalVariable *, GlobalVariable *>> UpgradedVariables;
   for (GlobalVariable &GV : TheModule->globals())
-    UpgradeGlobalVariable(&GV);
+    if (GlobalVariable *Upgraded = UpgradeGlobalVariable(&GV))
+      UpgradedVariables.emplace_back(&GV, Upgraded);
+  for (auto &Pair : UpgradedVariables) {
+    Pair.first->eraseFromParent();
+    TheModule->getGlobalList().push_back(Pair.second);
+  }
 
   // Force deallocation of memory for these vectors to favor the client that
   // want lazy deserialization.