[sancov] using comdat only when it is enabled

[aizatsky]

split trace-pc-guard test into two.

[aizatsky]

Kostya, please take a look.

I could suggest to remove all CHECKS but check for ctor from darwin but that wouldn't check the bulk of instrumentation.

It is also possible to extract only module_ctor checks into separate test but I'm not sure how useful it will be.

[aizatsky]

Actually, hold on a second, I'll replace the triple in darwin file, and that should take care of everything.

[aizatsky]

using target triple as intended.

[aizatsky]

Will reupload to add llvm-commits correctly

lib/Transforms/Instrumentation/SanitizerCoverage.cpp

if (HasSancovGuardsSection) {
       SecEnd->setVisibility(GlobalValue::HiddenVisibility);
 
       std::tie(CtorFunc, std::ignore) = createSanitizerCtorAndInitFunctions(
           M, SanCovModuleCtorName, SanCovTracePCGuardInitName,
           {Int32PtrTy, Int32PtrTy},
           {IRB.CreatePointerCast(SecStart, Int32PtrTy),
             IRB.CreatePointerCast(SecEnd, Int32PtrTy)});
 
+      if (TargetTriple.supportsCOMDAT()) {
         // Use comdat to dedup CtorFunc.
         CtorFunc->setComdat(M.getOrInsertComdat(SanCovModuleCtorName));
         appendToGlobalCtors(M, CtorFunc, SanCtorAndDtorPriority, CtorFunc);
+      } else {
+        appendToGlobalCtors(M, CtorFunc, SanCtorAndDtorPriority);
+      }
     }
   } else if (!Options.TracePC) {
     Function *CtorFunc;
     std::tie(CtorFunc, std::ignore) = createSanitizerCtorAndInitFunctions(
         M, SanCovModuleCtorName, SanCovModuleInitName,
         {Int32PtrTy, IntptrTy, Int8PtrTy, Int8PtrTy},
         {IRB.CreatePointerCast(RealGuardArray, Int32PtrTy),
          ConstantInt::get(IntptrTy, N),