[LTO] Always mark regular LTO units with EnableSplitLTOUnit=1 under the new pass manager

[leonardchan]

Summary

Match the behavior of D65009 under the new pass manager also.

[tejohnson]

Lgtm. Thanks for fixing this! Not sure how I missed doing this for both PMs.

As an aside, please upload future patches with context, it makes reviewing much easier.

clang/lib/CodeGen/BackendUtil.cpp

         if (!TheModule->getModuleFlag("ThinLTO"))
           TheModule->addModuleFlag(Module::Error, "ThinLTO", uint32_t(0));
         TheModule->addModuleFlag(Module::Error, "EnableSplitLTOUnit",
-                                 CodeGenOpts.EnableSplitLTOUnit);
+                                 uint32_t(1));
       }
       MPM.addPass(
           BitcodeWriterPass(*OS, CodeGenOpts.EmitLLVMUseLists, EmitLTOSummary));

clang/test/CodeGen/split-lto-unit.c

 // SPLIT: !{i32 1, !"EnableSplitLTOUnit", i32 1}
 //
 // ; Check that regular LTO has EnableSplitLTOUnit = 1
-// RUN: %clang_cc1 -flto -triple x86_64-pc-linux-gnu -emit-llvm-bc < %s | llvm-dis -o - | FileCheck %s --implicit-check-not="EnableSplitLTOUnit" --check-prefix=SPLIT
+// RUN: %clang_cc1 -fno-experimental-new-pass-manager -flto -triple x86_64-pc-linux-gnu -emit-llvm-bc < %s | llvm-dis -o - | FileCheck %s --implicit-check-not="EnableSplitLTOUnit" --check-prefix=SPLIT
+// RUN: %clang_cc1 -fexperimental-new-pass-manager -flto -triple x86_64-pc-linux-gnu -emit-llvm-bc < %s | llvm-dis -o - | FileCheck %s --implicit-check-not="EnableSplitLTOUnit" --check-prefix=SPLIT
 
 int main() {}