[ThinLTO] Ensure sanitizer passes are run

[tejohnson]

Summary

In ThinLTO compilation, we exit populateModulePassManager early and
were not adding PM extension passes meant to run at the end of the
pipeline. This includes sanitizer passes. Add these passes before
the early exit.

A test will be added to projects/compiler-rt.

[tejohnson]

ping

[pcc]

LGTM

lib/Transforms/IPO/PassManagerBuilder.cpp

if (RunInliner) {
     MPM.add(createGlobalOptimizerPass());
     MPM.add(createGlobalDCEPass());
   }
 
   // If we are planning to perform ThinLTO later, let's not bloat the code with
   // unrolling/vectorization/... now. We'll first run the inliner + CGSCC passes
   // during ThinLTO and perform the rest of the optimizations afterward.
   if (PrepareForThinLTO) {
+    // Ensure we perform any last passes, but do so before renaming anonymous
+    // globals in case the passes add any.
+    addExtensionsToPM(EP_OptimizerLast, MPM);
     // Rename anon globals to be able to export them in the summary.
     MPM.add(createNameAnonGlobalPass());
     return;
   }
 
   if (PerformThinLTO)
     // Optimize globals now when performing ThinLTO, this enables more
     // optimizations later.