InstrProf: Pack the coverage mapping structs that we write out

When we read this data we treat it as unaligned and packed, so we
should really be explicit about that when we write it.

llvm-svn: 241218

clang/lib/CodeGen/CoverageMappingGen.cpp

@@ -932,7 +932,7 @@ void CoverageMappingModuleGen::addFunctionMappingRecord(
   if (!FunctionRecordTy) {
     llvm::Type *FunctionRecordTypes[] = {Int8PtrTy, Int32Ty, Int32Ty, Int64Ty};
     FunctionRecordTy =
-        llvm::StructType::get(Ctx, makeArrayRef(FunctionRecordTypes));
+        llvm::StructType::get(Ctx, makeArrayRef(FunctionRecordTypes), true);
   }
 
   llvm::Constant *FunctionRecordVals[] = {