Fix COMPILE_PDB_NAME when used on an OBJECT library

When `COMPILE_PDB_NAME` is used without `COMPILE_PDB_OUTPUT_DIRECTORY`
we cannot fall back on the link `PDB_OUTPUT_DIRECTORY` for an object
library because it has no link step.

Fixes: #16674

Source/cmGeneratorTarget.cxx

@@ -1147,7 +1147,7 @@ std::string cmGeneratorTarget::GetCompilePDBPath(
 {
   std::string dir = this->GetCompilePDBDirectory(config);
   std::string name = this->GetCompilePDBName(config);
-  if (dir.empty() && !name.empty()) {
+  if (dir.empty() && !name.empty() && this->HaveWellDefinedOutputFiles()) {
     dir = this->GetPDBDirectory(config);
   }
   if (!dir.empty()) {

Tests/ObjectLibrary/A/CMakeLists.txt

@@ -21,3 +21,4 @@ add_custom_command(
 
 add_library(A OBJECT a1.c a2.c a.cmake)
 target_include_directories(A PRIVATE ${CMAKE_CURRENT_SOURCE_DIR})
+set_property(TARGET A PROPERTY COMPILE_PDB_NAME Apdb)