Revert "make -fmodules-codegen and -fmodules-debuginfo work also with PCHs"

This caused PR44953. See also the discussion on D74846.

This reverts commit cbc9d22e49b434b6ceb2eb94b67079d02e0a7b74.
diff --git a/clang/lib/Serialization/ASTWriterDecl.cpp b/clang/lib/Serialization/ASTWriterDecl.cpp
index 472136d..92d566f 100644
--- a/clang/lib/Serialization/ASTWriterDecl.cpp
+++ b/clang/lib/Serialization/ASTWriterDecl.cpp
@@ -1011,16 +1011,15 @@
 
   if (D->getStorageDuration() == SD_Static) {
     bool ModulesCodegen = false;
-    if (!D->getDescribedVarTemplate() && !D->getMemberSpecializationInfo() &&
+    if (Writer.WritingModule &&
+        !D->getDescribedVarTemplate() && !D->getMemberSpecializationInfo() &&
         !isa<VarTemplateSpecializationDecl>(D)) {
       // When building a C++ Modules TS module interface unit, a strong
       // definition in the module interface is provided by the compilation of
       // that module interface unit, not by its users. (Inline variables are
       // still emitted in module users.)
       ModulesCodegen =
-          (((Writer.WritingModule &&
-             Writer.WritingModule->Kind == Module::ModuleInterfaceUnit) ||
-            Writer.Context->getLangOpts().BuildingPCHWithObjectFile) &&
+          (Writer.WritingModule->Kind == Module::ModuleInterfaceUnit &&
            Writer.Context->GetGVALinkageForVariable(D) == GVA_StrongExternal);
     }
     Record.push_back(ModulesCodegen);
@@ -2449,11 +2448,9 @@
 
   assert(FD->doesThisDeclarationHaveABody());
   bool ModulesCodegen = false;
-  if (!FD->isDependentContext()) {
+  if (Writer->WritingModule && !FD->isDependentContext()) {
     Optional<GVALinkage> Linkage;
-    if ((Writer->WritingModule &&
-         Writer->WritingModule->Kind == Module::ModuleInterfaceUnit) ||
-        Writer->Context->getLangOpts().BuildingPCHWithObjectFile) {
+    if (Writer->WritingModule->Kind == Module::ModuleInterfaceUnit) {
       // When building a C++ Modules TS module interface unit, a strong
       // definition in the module interface is provided by the compilation of
       // that module interface unit, not by its users. (Inline functions are