[ThinLTO/Summary] Rename anonymous globals as last action in the per-TU -O0 pipeline

[davide]

Summary

The problem is that there could be passes registered using addExtensionsToPM() introducing unnamed globals.
Asan is an example, but there may be others. Building cppcheck with -thinlto and -fsanitize=address triggers an assertion while we're reading bitcode (in lib/LTO), as the BitcodeReader while reading the summary assumes there are no unnamed globals because the namer has run).
Unfortunately I wasn't able to find an easy way to test this. I added a comment in the hope nobody moves this again, but, if folks have a way to test, I'm all ears.

Fixes https://bugs.llvm.org/show_bug.cgi?id=32004

[mehdi_amini]

LGTM.

lib/Transforms/IPO/PassManagerBuilder.cpp

if (OptLevel == 0) {
     // that pass manager. To prevent this we insert a no-op module pass to reset
     // the pass manager to get the same behavior as EP_OptimizerLast in non-O0
     // builds. The function merging pass is
     if (MergeFunctions)
       MPM.add(createMergeFunctionsPass());
     else if (!GlobalExtensions->empty() || !Extensions.empty())
       MPM.add(createBarrierNoopPass());
 
-    if (PrepareForThinLTO)
-      // Rename anon globals to be able to export them in the summary.
+    addExtensionsToPM(EP_EnabledOnOptLevel0, MPM);
+
+    // This has to be done after we add the extensions to the pass manager
+    // as there could be passes (e.g. Adddress sanitizer) which introduce
+    // new unnamed globals.
+    if (PrepareForThinLTO)
       MPM.add(createNameAnonGlobalPass());
-
-    addExtensionsToPM(EP_EnabledOnOptLevel0, MPM);
     return;
   }
 
   // Add LibraryInfo if we have some.
   if (LibraryInfo)
     MPM.add(new TargetLibraryInfoWrapperPass(*LibraryInfo));
 
   addInitialAliasAnalysisPasses(MPM);